Liquid crystal display

ABSTRACT

A liquid crystal display device includes first and second substrates, a liquid crystal layer disposed therebetween, pixel regions formed by gate signal lines and image signal lines formed over the first substrate, a first insulating layer formed over the gate signal lines, thin film transistors connected to the gate signal lines with in a second insulating layer formed thereover, pixel electrodes connected to the thin film transistors, a counter electrode formed of a first transparent conductive layer over the second insulating layer, and a second transparent conductive layer and an external connection terminal disposed outside of the pixel regions. The second transparent conductive layer is formed over the second insulating layer and is electrically connected to the counter electrode and the external connection terminal, and a part of each of the gate signal lines is disposed outside of the pixel regions and is covered by the second transparent conductive layer.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 13/206,951, filedAug. 10, 2011, now U.S. Pat. No. 8,233,126, which is a continuation ofU.S. application Ser. No. 12/760,902, filed Apr. 15, 2010, now U.S. Pat.No. 8,027,005, which is a continuation of U.S. application Ser. No.12/395,805, filed Mar. 2, 2009, now abandoned, which is a continuationof U.S. application Ser. No. 11/591,510, filed Nov. 2, 2006, now U.S.Pat. No. 7,612,853, which is a continuation of U.S. application Ser. No.11/239,198, filed Sep. 30, 2005, now abandoned, which is a continuationof U.S. application Ser. No. 10/219,391, filed Aug. 16, 2002, now U.S.Pat. No. 6,975,374, which is a continuation of U.S. application Ser. No.09/803,980, filed Mar. 13, 2001, now U.S. Pat. No. 6,462,799, which is acontinuation of U.S. application Ser. No. 09/331,266, filed Jun. 18,1999, now U.S. Pat. No. 6,532,053, which is a 371 of PCT/JP96/03691,filed Dec. 18, 1996, and with U.S. application Ser. No. 09/804,190,filed Mar. 13, 2001, now U.S. Pat. No. 6,831,724, the subject matter ofwhich is incorporated by reference herein. This application is relatedto U.S. Ser. No. 13/206,988, filed Aug. 10, 2011, which is copendingwith U.S. Ser. No. 13/206,951.

BACKGROUND OF THE INVENTION

The present invention relates generally to active-matrix liquid crystaldisplay devices and, more particularly, to liquid crystal displaydevices of the lateral electric field type having wide view-anglecharacteristics suitable for improvement of the aperture ratio.

Liquid crystal display devices of the active matrix type, which employactive elements typically, including thin-film transistors (TFTS), arebecoming more important in the manufacture of display terminals for usewith OA equipment in view of the fact that these devices offer enhanceddisplayability with superior image quality in comparison to cathode raytubes, not to mention the flatness and light-weight features thereof.Such liquid crystal display devices are generally categorized into twotypes.

In one type, a liquid crystal material is sandwiched between twosubstrates, with a plurality of transparent electrodes being arrangedthereon, so that application of a voltage to such transparent electrodecauses an electric field to be generated transverse to the substrate,thereby modulating rays of light falling onto the liquid crystal afterpassing through the transparent electrodes, to thereby generate adisplay—all of the currently available products are designed to employthis scheme.

The other type of device was a scheme for causing the liquid crystal tobe modulated by an electric field that is generated substantially inparallel to a substrate surface between two electrodes arranged on thesame substrate, thereby modulating light incident on the liquid crystalfrom a space between the two electrodes, to thereby generate a displayin which the viewing angle is extremely wide. This technology, whichshows great promise for improvements in active-matrix liquid crystaldisplay devices, is called a “lateral electric field” type or,alternatively, an “in-plane switching” type device.

Some features of the latter type of device have been disclosed inDomestically Published Japanese PCT Application No. 5-505247 PublishedJapanese Patent Application No. 63-21907 (JP-A-63-21907), andJP-A-6-160878.

However, in the in-plane switching type device, since an opaque metalelectrode is arranged into a comb-like shape on one substrate, theresulting ratio of the opening region permitting light to passtherethrough (aperture ratio) is significantly low, which results in theproblem that active-matrix liquid crystal display devices of thein-plane switching type have a display screen which is dark, or,alternatively, a bright backlight with great power dissipation must beused in order to brighten the display screen, resulting in an increasein the power dissipation of the devices.

Another problem associated with the in-plane switching type device isthat the use of a metal electrode leads to an increase the reflectivityat the electrode, which in turn creates a problem in that an image orthe like appears like a ghost image on the screen due to reflection atthe electrode, reducing the recognizability of the display.

SUMMARY OF THE INVENTION

The present invention is designed to solve the problems mentioned above,and an objective of the present invention is to provide an active-matrixliquid crystal display device employing the in-plane switching scheme,which device is capable of realizing a viewing angle equivalent to thatof cathode ray tubes, and wherein the active-matrix liquid crystaldisplay device is bright due to a high aperture ratio and yet is low inpower dissipation and in reflection for achieving increaseddisplayability.

To attain the foregoing object, the present invention offers, as itsfirst aspect, an arrangement in which at least one of a pixel electrodeand a counter electrode is provided as a transparent electrode; thenormally-black mode is established for providing dark display in theabsence of an electric field as applied thereto; the initial alignmentstate of the twistable liquid crystal layer is the homogeneous alignmentstate upon application of no electric fields; liquid crystal moleculesbetween said electrodes and those on the electrodes upon application ofan electric field rotate controllably in a direction substantiallyparallel to the substrate surface; the maximum value of the opticaltransmissivity of a liquid crystal display panel is 4.0% or greater;and, the view-angle range of the contrast ratio of 10 to 1 or greater iswithin the range of all-directional coverage as tilted by 40 degrees ormore from the vertical direction relative to the display plane.

As a second aspect of the invention, at least one of the pixel electrodeand counter electrode is provided as a transparent electrode, thenormally-black mode is set for providing dark display upon applicationof no electric fields, the initial alignment state of the twistableliquid crystal layer is the homogeneous state upon application of noelectric fields, and the twist elastic modulus is not greater than10×10⁻¹² N (Newton).

As a third aspect of the invention, at least one of the pixel electrodeand counter electrode is provided as a transparent electrode, thenormally-black mode is set for providing dark display upon applicationof no electric fields, the initial alignment state of the twistableliquid crystal layer is the homogeneous state upon application of noelectric fields, the initial pretilt angle of those liquid crystalmolecules at the upper and lower interfaces of the liquid crystal layeris not more than 10 degrees, and the initial tilt state of liquidcrystal molecules within the liquid crystal layer are in the splaystate.

As a fourth aspect of the invention, at least one of the pixel electrodeand counter electrode is provided as a transparent electrode, thenormally black mode is set for providing dark display upon applicationof no electric fields, the initial alignment state of the twistableliquid crystal layer is the homogeneous state upon application of noelectric fields, and the average tilt angle of liquid crystal moleculesof the liquid crystal layer on the transparent electrode is less than 45degrees even when applying an electric field thereto.

As a fifth aspect of the invention, in any one of the arrangementsdescribed above, a double structure of a transparent electrode and anopaque electrode is employed for at least either the pixel electrode orthe counter electrode.

As a sixth aspect of the invention, in any one of the arrangementsdescribed above, a structure is used in which neighboring ones ofcontra-voltage signal lines are connected by a counter electrode withina pixel via more than one through-hole.

As a seventh aspect of the invention, in any one of the arrangementsdescribed above, a protective film is provided for use in covering orcoating active matrix elements, and at least one of said pixel electrodeor said counter electrode is formed overlying said protective film whilepermitting electrical connection via more than one through-hole asformed in said protective film to either active matrix elements orcontra-voltage signal lines.

As an eighth aspect of the present invention, in any one of thearrangements described above, the counter electrode is made of atransparent electrode, and further use is made of a structure having anoptical shield pattern between a counter electrode and an image signalline.

As a ninth aspect of the invention, in any one of the arrangementsdescribed above, the contra-voltage signal line for electricalconnection between counter electrodes is made of a metal.

As a tenth aspect of the invention, in any one of the arrangementsdescribed above, more than three counter electrodes are formed, two ofwhich are formed adjacent to image signal lines, wherein the counterelectrodes formed adjacent to the image signal lines are opaque.

As an eleventh aspect of the invention, in any one of the arrangementsdescribed above, a transparent conductive film for use as thetransparent electrode is made of indium-tin-oxide (ITO).

As a twelfth aspect of the invention, the contra-voltage signal line ismade of Cr, Ta, Ti, Mo, W, Al, or an alloy thereof, or, alternatively, aclad structure with such materials laminated.

As a thirteenth aspect of the invention, the contra-voltage signal lineis a clad structure with a transparent conductive film such asindium-tin-oxide (ITO) or the like being laminated on Cr, Ta, Ti, Mo, W,Al, or an alloy thereof.

As a fourteenth aspect of the invention, in any one of the arrangementsdescribed above, the initial twist angle of said liquid crystal layer issubstantially zero, wherein the initial alignment angle is greater thanor equal to 45 degrees and yet less than 90 degrees when the dielectricanisotropy Δ∈ of the liquid crystal material is positive in polarity,whereas it goes beyond zero degree and stays less than 45 degrees if thedielectric anisotropy Δ∈ is negative.

As a first manufacturing method, the invention is featured by forming atleast any one of a scan signal line end section, an image signal lineend section or the uppermost layer of a counter electrode end sectionand at least one of a pixel electrode or counter electrode as atransparent conductive layer, and further by forming them in the sameprocess step.

An example of the features of the present invention will be set forthbelow.

First of all, according to the first aspect of the invention, at leastone of the pixel electrode or its counter electrode is made transparentto increase the light penetrating such portion, thereby to effectimprovement of the maximum optical permeability or transmissivity duringbright (white) display and make it possible to produce a brighterdisplay than in cases where the electrodes are opaque so that the liquidcrystal display panel's transmissivity can be improved in the value ofthe maximum transmissivity from 3.0 to 3.8%, in the case of employingopaque electrodes, to up to 4.0% or greater in accordance with thepresent invention. More specifically, assuming that the brightness orluminance of backlight incident light is at 3,000 cd/m² the maximumbrightness value of bright-display luminance can attain 120 cd/m² orgreater.

Further, as the liquid crystal molecules retain their initialhomogeneous alignment state upon application of no voltages, when thelayout of polarizer plates is designed to establish dark (black) displayin such state (in normally-black mode), no rays of light pass throughsuch portion even where the electrodes are made transparent, therebymaking it possible to achieve a dark display of good quality, thusimproving the contrast.

On the contrary, if the normally-white mode is set then dark displayingmust be carried out upon application of a voltage, which results in aninability to completely block the light at portions overlying theelectrodes upon application of a voltage, which in turn makes itimpossible to provide a dark display with good quality due to the factthat the transmitted light at such portions increases the transmissivityof the dark display. For this reason, a sufficient contrast ratio cannotbe attained.

Furthermore, wide viewing angle characteristics can be obtained becausethose liquid crystal display molecules between said electrodes and overthe electrodes upon application of a voltage thereto behave tocontrollably rotate in a direction parallel to the substrate surfaces.

Accordingly, wide view-angle characteristics can be obtained in whichthe view-angle range of contrast ratios of 10 to 1 or more falls withinan all-directional range with an inclination of 40 degrees or greaterfrom the vertical direction with respect to the display plane.

According to the second aspect of the invention, the twist elasticmodulus of a twistable liquid crystal layer is less than or equal to10×10⁻¹² N (Newton) when applying a voltage between the pixel electrodeand counter electrode, the angle α of rotation from the initialalignment direction increases on or over a transparent conductive filmto allow the on-electrode transmissivity to complementally interact withthe transmissivity between electrodes to substantially improve theaperture ratio. It is preferable that this twist elastic modulus K2 besmaller.

According to the third aspect of the invention, in view of the fact thatthe initial pretilt angle of liquid crystal molecules at the upper andlower interfaces of a liquid crystal layer is less than or equal to 10degrees, while the initial tilt state of liquid crystal molecules insideof the liquid crystal layer is in a splay state, the tilt angle ofliquid crystal molecules at the center of the liquid crystal layerbecomes nearly zero degrees to thereby enable the liquid crystal layercontributing to the display to decrease in average tilt angle; thus,even upon application of a voltage, it becomes possible to establish lowtilt angles of those liquid crystal molecules between electrodes andover transparent electrodes, which in turn makes it possible to realizeboth aperture ratio improvement and wide viewing angles.

According to the fourth aspect of the invention, both aperture ratioimprovement and wide viewing angles can be realized due to the fact thatthe average tilt angle of the liquid crystal layer's liquid crystalmolecules on or over the transparent electrode stays below 45 degreeseven when applying a voltage thereto.

According to the fifth aspect of the invention, the use of a double orduplex structure of a transparent electrode and opaque metal electrodefor either the pixel electrode or the counter electrode makes itpossible to greatly prevent short-circuiting defects at this electrode,which will be advantageous for achievement of large screens.

According to the sixth aspect of the invention, the use of a structurefor letting neighboring contra-voltage signal lines be connected by acounter electrode within a pixel via more than one through-hole permitsrespective contra-voltage signal lines to be electrically connectedtogether in a net-mesh-like pattern, which makes it possible to reducethe resistivity of such contra-voltage signal lines, wherein seriousdefects will no longer take place even upon occurrence of open circuitfailures.

The seventh aspect of the invention lies in an ability to let theprotective film suppress reduction of an electric field acting on liquidcrystal molecules, which makes it possible to lower the drivevoltage(s).

According to the eighth aspect of the invention, the aperture ratio isimproved by use of a structure in which the counter electrode made of atransparent electrode and an optical shield pattern is provided betweenthe counter electrode and its associative image signal line(s).

According to the ninth aspect of the invention, lowering the resistivityof contra-voltage signal lines makes it possible to smoothen thetransmission of a voltage between counter electrodes, thus reducingdistortion of the voltage, which in turn enables suppression ofcross-talk in the horizontal direction.

According to the tenth aspect of the invention, by making the counterelectrode neighboring upon image signal lines opaque will suppresscrosstalk associated with image signals.

The reason for this is set forth below.

Forming a transparent counter electrode in close proximity to an imagesignal line forces an electric field (electric flux lines) from theimage signal line to be absorbed by the counter electrode, with a resultthat the electric field from the image signal line hardly affects theelectric field generated between the pixel electrode and counterelectrode to thereby extremely suppress generation of crosstalkassociated with image signals in particular, crosstalk in the up/downdirection of the substrates concerned. However, the behavior of theliquid crystal molecules on or over the counter electrode neighboringupon the image signal line is unstable due to variation of imagesignals; and, if the counter electrode that neighbors the image signalline is made transparent, then crosstalk is observed due to transmittedlight at such an electrode portion. Accordingly, letting the counterelectrode adjacent to the image signal line be opaque makes it possibleto suppress crosstalk associated with image signals.

According to the eleventh aspect of the present invention, thetransparent conductive film is indium-tin-oxide (ITO), which is suitablefor improvement of the optical transmissivity.

According to the twelfth and thirteenth aspects of the presentinvention, the contra-voltage signal line is a laminated clad structure,and the resistance value decreases enabling reduction of open circuitdefects.

According to the fourteenth aspect of the present invention, because theliquid crystal layer's initial twist angle is nearly zero, while theinitial alignment angle is greater than or equal to 45° C., and yet isless than 90° C. if the dielectric anisotropy Δ∈ is positive in polarityand is above 0°, and yet is less than or equal to 45° if the dielectricanisotropy Δ∈ is negative, it is possible to improve the contrast bysuppressing the domain and optimizing the range of a maximal applicationvoltage, while at the same time enabling optimization of the responsespeed.

The first manufacturing method is designed to enable fabrication ofpixel electrodes and counter electrodes using transparent conductivefilms without increasing the required number of process steps, bysimultaneously forming both the transparent conductive layer of a scansignal line terminate end portion, an image signal line end, or thecounter electrode end's uppermost-layer and the transparent conductivefilm of the pixel electrode or counter electrode.

It should be noted that although the liquid crystal display device ofthe present invention is designed so that at least one of the pixelelectrode and the counter electrode is formed of a transparentconductive film, a difference in configuration from a liquid crystaldisplay device as recited in, for example, Richard A. Soref, Proceedingsof the IEEE, December issue, 1974 at pp. 1710-1711 (referred to as“Reference 1” hereinafter) is as follows.

In Reference 1, a comb-shaped electrode corresponding to a pixelelectrode and counter electrode is constituted from a transparentconductive film.

However, when forming the initial alignment state of liquid crystalmolecules, SiO (silicon mono-oxide) is orthorhombically deposited atabout 85 degree to intentionally form extremely high pretilt angles atthe liquid crystal molecules in the interface between each electrode andthe liquid crystal layer. For this reason, as shown in FIG. 1(b) ofReference 1, applying a voltage between comb-shaped electrodes from thehomogeneous alignment with 90-degree twisting in the initial alignmentstate results in formation, as the realignment state, of a homogeneousalignment state that is substantially parallel to substrate surfaces ina region between the electrodes and of a homeotropic alignment statethat is perpendicular to substrate surfaces in a region on or above theelectrodes.

However, with this arrangement, there is a drawback in that, althoughcomplementary interaction of the two kinds of liquid-crystal moleculerealignment states with an increase in electric field might result inachievability of brighter display, the resultant viewing anglecharacteristic becomes narrower due to a need to averagely increase thetilt angle of liquid crystal molecules.

On the contrary, with the liquid crystal display device of the lateralelectric field type in accordance with the present invention, a specificconfiguration is employed wherein even when applying a voltage betweenthe pixel electrode and counter electrode in order to obtain a wideview-angle characteristic and a good aperture ratio, those realigningportions of liquid crystal molecules contributing to a display image areforced to retain the homogeneous alignment state that maximallyparallels the substrate surfaces while simultaneously letting, on orover electrodes of a transparent conductive film, the on-electrodetransmissivity complementary interact with the interelectrodetransmissivity in a way corresponding to the angle α of rotation fromthe initial alignment direction, resulting in substantial improvement ofthe aperture ratio.

It should be noted that in the description, the term “homogeneousalignment state” refers to a state in which the liquid crystal moleculeswithin a liquid crystal layer have a tilt (rise-up) angle lyingmaximally parallel to either the substrate surface or the interface ofsuch liquid crystal layer are practically, a specific alignment state inwhich the tilt angle from either the substrate surface or the liquidcrystal layer's interface stays below 45 degrees. Accordingly, the“homeotropic alignment state” is defined as a case in which the tiltangle from either the substrate surface or the liquid crystal layer'sinterface exceeds 45 degrees.

FIG. 41A shows an example of a voltage potential distribution within aliquid crystal layer in an electrode arrangement for creation of anelectric field extending nearly parallel to the substrate surface.

Solid lines in the drawing designate equal-potential lines, wherein anelectric-field vector is given in a direction perpendicular to suchequal-potential lines. While the electric field vector E permitsproduction of only components Ey extending at right angles to thesubstrate surface on the electrode center, those components Ex extendinghorizontally relative to the substrate surface also appear in theremaining part other than the center. In a region in which suchhorizontal components, i.e. lateral electric field components-Ex arebeing generated, liquid crystal molecules between the electrodes behaveto rotate through a rotation angle α from the initial alignmentdirection RDR in the direction of the lateral electric field Ex as shownin FIGS. 41B and 41C.

On the other hand, on-electrode liquid crystal molecules behave torotate with a rotation of the interelectrode liquid crystal molecules inthe presence of a molecular field. Accordingly, although no lateralelectric field is being applied to the central on-electrode liquidcrystal molecules, these molecules attempt to rotate due to themolecular field in the same direction as that of their outlying liquidcrystal molecules. In other words, the rotation angle α is large betweenthe electrodes, decreases at locations on or above the electrodes, andbecomes maximal over the electrode center portion.

A result of simulating this manner of operation is shown in FIGS.42A-42C.

Note here that the simulation in this example was carried out using anexemplary arrangement in which the liquid crystal molecules' initialhomogeneous alignment state is designed so that the liquid crystallayer's initial twist angle is substantially zero, whereas an initialalignment angle defined between the initial alignment direction RDR andthe applied electric field Ex is set at φLC=75 degrees, while lettingthe initial pretilt angle of certain liquid crystal molecules near oraround the liquid crystal layer's upper and lower interfaces be set atzero degrees, and further employing a Cross Nicol layout that lets thetransmission axis of one of polarizer plates be identical to saidinitial alignment direction RDR with the transmission axis of the otherpolarizer plate being at right angles, thereby performing displaying ina double refraction mode.

The optical transmissivity T/T₀ at this time may be represented by thefollowing equation:T/T ₀=sin²(2αeff)·sin²(πdeff×Δn/λ).  (1)Here, αeff is the angle defined between the liquid crystal layer'seffective light axis and the polarized-light transmission axis—in thisexample, this is the net value of the liquid crystal molecule rotationangle α in the direction along the thickness direction of the liquidcrystal layer, which is a “virtual” value that is treatable as theaverage value under an assumption that the rotation is uniform.

Additionally, deff is the effective thickness of a liquid crystal layerhaving double-refractivity, Δn is the refractive anisotropy, and λ isthe wavelength of light.

In Equation (1), at the time of application of an electric field Ex, thevalue of αeff increases with an increase in the intensity thereof, andbecomes maximal at 45 degrees.

Furthermore, in the simulation of this example, the liquid crystallayer's retardation Δn·deff is set at a selected value that is half ofthe wavelength λ of light for achievement of the double refractionzero-order mode, while setting the dielectric anisotropy Δ∈ to apositive polarity.

FIG. 42A is a characteristic diagram showing the state ofequal-potential lines in the case of applying to a transparent ITOelectrode a voltage at which bright display near the maximum isobtainable, wherein the vertical axis represents the thickness (4.0 μmthick) of a liquid crystal layer and the transverse axis indicates arelative electrode positional relationship. Note that the values in thisdrawing are indicative of the voltage potential strength standardized.

Also see FIG. 42B and FIG. 42C, which show the rotation angle α and tilt(rise-up) angle of liquid crystal molecules within a liquid crystallayer upon application of lateral electric field components Ex as formedfrom the state of the equal-potential lines.

As shown in FIG. 42C, the on-electrode liquid crystal molecules hardlyrise up even when applying a voltage thereto. In this example, the tiltangle stays below 8° in the entire direction along the thickness of theliquid crystal layer. Further, as shown in FIG. 42B, those liquidcrystal molecules on or over the electrodes also have rotated about 15to 35°. It is noted that the sign of the tilt angle shown in FIG. 42C isdetermined so that the rightward rise-up in the drawing is positivewhereas leftward rise-up is negative for purposes of convenience inillustration and discussion herein. Therefore, with the scheme of thepresent invention, it becomes possible to allow the liquid crystalmolecules to vary in rotation angle α even on or over the electrodes tothereby change the transmissivity.

The one character that is most pertinent to this operation is the liquidcrystal is twist elastic modulus K2, which is preferably as small aspossible in view of the fact that as this modulus K2 gets smaller,liquid crystal molecules on or over electrodes receive influence of theinterelectrode liquid crystal molecules to rotate approaching therotation angle α of such interelectrode liquid crystal molecules.

Referring to FIG. 41D, there is shown a model of a distribution of theon-electrode transmissivity and the interelectrode transmissivity in acase where the twist elastic modulus K2 is set at about 10×10⁻¹² N(Newton).

In case the electrodes concerned are transparent, the on-electrodeliquid crystal molecules' realignment operation discussed above allows 5to 30% of the average transmissivity of transmissivities at part “A”between electrodes to become the average-value transmissivity oftransmissivities at part “B” on or over the electrodes.

In addition, as will be described later, it has been found that if thetwist elastic modulus K2 is less than or equal to 2.0×10⁻¹² N (Newton),then more than 50% of the average transmissivity of transmissivities atthe part “A” between the electrodes becomes equal to the average-valuetransmissivity of transmissivities at the part B on or over theelectrodes. Therefore, the average transmissivity over the entire partis raised up to become the average-value transmissivity of thetransmissivities at the A+B portions.

In summary, when compared to electrodes which have been traditionallycomprised of a metal layer that permits no light rays to pass through,it becomes possible to substantially improve the aperture ratio perpixel.

With the simulation of this example, calculation is carried out with theinitial pretilt angle being set at zero degrees; however, in actualimplementation, it will be required that the initial pretilt angle nearor around the interfaces of the liquid crystal layer with itsassociative alignment film(s) be set by rubbing treatment atapproximately 10 degrees or less; and, more preferably, it is set at 6degrees or below. Additionally, in an embodiment to be later described,it is set at about 5 degrees.

With the initial pretilt angle falling within such a range, it ispossible to control the liquid crystal molecules at the liquid crystallayer interfaces so that they align in the substrate in-plane direction,thereby making it possible to allow the average tilt angle of the liquidcrystal layer on or over electrodes to stay below 45 degrees even uponapplication of electric fields thereto. In other words, it becomespossible even when applying electric fields to prevent on-electrodeliquid crystals from exhibiting so-called homeotropic alignment.

FIG. 44 is an example of a characteristic diagram of a simulationresult, which shows tilt angles of liquid crystal molecules within aliquid crystal layer in the liquid crystal display device of the lateralelectric field type, along with a view-angle range in which the contrastratio becomes 10 or greater in all directions concerned.

More specifically, even when the tilt angle is about 30 degrees, theresultant contrast ratio stays at or above 10 in all the directionswithin the view-angle range with about 40-degree inclination from thevertical direction relative to the display plane, which results inachievement of the intended characteristics that are substantiallyidentical to those in prior art liquid crystal display devices of thelongitudinal electric-field type. Furthermore, the less the tilt angle,the greater will be the view-angle range. If the former is about 10degrees, then the latter expands to exhibit a view-angle range withinclination of about 80 degrees; whereas, if the former is 5 degrees orless, then the latter expands to fill almost the entire range—thus, wideview-angle characteristics are obtained.

In this embodiment, since this aspect of the invention is designed toreduce at any event the average tilt angle of the liquid crystalmolecules within the liquid crystal layer between the electrode and onor over the transparent electrode when applying no electric fields andwhen applying an electric field thereto, the rubbing direction ofalignment films ORI1, ORI2 to be later described are set in an initialalignment state so that the initial pretilt angle of the liquid crystalmolecules at the interfaces of the liquid crystal layer on the sides ofthe two substrates SUB1, SUB2 is in a splay state to thereby ensure thatcertain liquid crystal molecules at or near the center of the liquidcrystal layer exhibit maximized parallelism with respect to theinterfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic plan view of a main part of one pixel alongwith nearby portions of a liquid crystal display section of a colorliquid crystal display device of the active matrix type in accordancewith an embodiment 1 of the present invention.

FIG. 2 is a diagrammatic sectional view of the pixel taken along line3-3 of FIG. 1.

FIG. 3 is a diagrammatic sectional view of a thin-film transistorelement TFT taken along line 4-4 of FIG. 1.

FIG. 4 is a diagrammatic sectional view of a storage capacitor Cstgtaken along line 5-5 of FIG. 1.

FIG. 5 is a plan view illustrating an arrangement of a matrix peripheralsection of a display panel.

FIG. 6 is a diagrammatic sectional view showing panel edge sections witha scan signal terminal on its left-hand side and without any externalconnection terminal on the right-hand side thereof.

FIG. 7A is a diagrammatic plan view showing a nearby part of aconnection section of a gate terminal GTM and gate lead GL; and FIG. 7Bis a side sectional view thereof.

FIG. 8A is a diagrammatic plan view showing a nearby part of aconnection section of a drain terminal DTM and image signal line DL; andFIG. 8B is a side sectional view thereof.

FIG. 9A is a diagrammatic plan view showing a nearby part of aconnection section of a common electrode terminal CTM and common busline CB as well as common voltage signal line CL; and FIG. 9B is a sidesectional view thereof.

FIG. 10 is a circuit diagram including a matrix section and itsperiphery of the active-matrix color liquid crystal display device ofthe present invention.

FIG. 11 is a diagram showing drive waveforms of the active-matrix colorliquid crystal display device of the present invention.

FIG. 12 is a flow chart showing some major steps A-C in the manufactureof a substrate SUB1 side part along with corresponding sectional viewsof a pixel section and of a gate terminal section.

FIG. 13 is a flow chart showing some major steps D-F in the manufactureof the substrate SUB1 side part along with corresponding sectional viewsof the pixel section and gate terminal section.

FIG. 14 is a flowchart showing some major steps G-H in the manufactureof the substrate SUB1 side part along with corresponding sectional viewsof the pixel section and gate terminal section.

FIG. 15 is a diagrammatic top plan view showing the state in whichperipheral drive circuitry is mounted on a liquid crystal display panel.

FIG. 16 is a diagrammatic sectional view of a tape carrier package TCPin which an integrated circuit chip CH1 constituting driver circuitry ismounted on a flexible printed circuit board.

FIG. 17 is a main-part sectional view showing the state in which thetape carrier package TCP is connected to a scan signal circuit terminalGTM of a liquid crystal display panel PNL.

FIG. 18 is an exploded perspective view of a liquid crystal displaymodule.

FIG. 19 is a diagram showing a relation of an electric field applicationdirection and a rubbing direction as well as a polarizer plate'spenetration axis.

FIG. 20 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 2 of the presentinvention.

FIG. 21 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 3 of the presentinvention.

FIG. 22 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 4 of the presentinvention.

FIG. 23 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 5 of the presentinvention.

FIGS. 24A-C are partial main-part plan view, a sectional view and amain-part plane view, respectively, which show one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 6 of the presentinvention.

FIG. 25 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 7 of the presentinvention.

FIG. 26 is a sectional view taken along a line 6-6 of FIG. 25.

FIG. 27 is a sectional view of a thin-film transistor element TFT takenalong line 7-7 of FIG. 25.

FIG. 28 is a sectional view of a storage capacitor Cstg taken along line8-8 of FIG. 25.

FIG. 29A is a plan view showing a nearby part of a connection section ofa gate terminal GTM and gate lead GL; and FIG. 29B is a sectional viewthereof.

FIG. 30A is a plan view showing a nearby part of a connection section ofa drain terminal DTM and image signal line DL; and FIG. 30B is asectional view thereof.

FIG. 31A is a plan view showing a nearby part of a connect section of acommon electrode terminal CTM1 and common bus line CB1 as well as commonvoltage signal line CL; and FIG. 31B is a sectional view thereof.

FIG. 32A is a plan view showing a nearby part of a connect section of acommon electrode terminal CTM2 and common bus line CB2 plus commonvoltage signal line CL; and FIG. 32B is a sectional view thereof.

FIG. 33 is a circuit diagram including a matrix section and itsperiphery of the active-matrix color liquid crystal display device ofthe present invention.

FIG. 34 is a diagram showing drive waveforms of the active-matrix colorliquid crystal display device of the present invention.

FIG. 35 is a flow chart showing some major steps A-C in the manufactureof a substrate SUB1 side part along with corresponding sectional viewsof a pixel section and of a gate terminal section.

FIG. 36 is a flowchart showing some major steps D-E in the manufactureof the substrate SUB1 side part along with corresponding sectional viewsof the pixel section and gate terminal section.

FIG. 37 is a flowchart showing a step F in the manufacture of thesubstrate SUB1 side part along with corresponding sectional views of thepixel section and gate terminal section.

FIG. 38 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 8 of the presentinvention.

FIG. 39 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 9 of the presentinvention.

FIG. 40 is a main-part plan view showing one pixel along with itsoutlying part of a liquid crystal display section of an active-matrixcolor liquid crystal display device of an embodiment 10 of the presentinvention.

FIGS. 41A-D are diagrams showing principles of the present invention,wherein FIG. 41A is a characteristic diagram showing a voltage potentialdistribution within a liquid crystal layer when a voltage is applied toelectrodes, FIG. 41B is a diagram showing a realignment state of thoseliquid crystal molecules near or around the center of the liquid crystallayer, FIG. 41C is a characteristic diagram showing rotation angles α ofliquid crystal molecules shown in FIG. 41B, and FIG. 41D is oneexemplary characteristic diagram showing a distribution of thetransmissivity of rays of light passing through the liquid crystal layeron or over the upper and lower polarizer plates and upper/lowersubstrates plus electrodes as well as between electrodes concerned.

FIG. 42A is a characteristic diagram showing the state ofequal-potential “contour” lines each connecting the points of the samepotential when applying a voltage to a transparent electrode, whereasFIG. 42B and FIG. 42C show one example of the rotation angle α of liquidcrystal molecules within a liquid crystal layer upon application of anelectric field thereto along with the tilt (rise-up) angle thereof.

FIGS. 43A to 43D are diagrams showing principles relating to improvementof the aperture ratio of an active-matrix color liquid crystal displaydevice in accordance with an embodiment 11 of the present invention,wherein FIG. 43A is a characteristic diagram showing a voltage potentialdistribution within a liquid crystal layer when a voltage is applied toan electrodes), FIG. 43B is a diagram showing a realignment state ofthose liquid crystal molecules near or around the center of the liquidcrystal layer, FIG. 43C is a characteristic diagram showing rotationangles α of liquid crystal molecules shown in FIG. 43B, and FIG. 43D isan example of a characteristic diagram showing a distribution of thetransmissivity of rays of light passing through a liquid crystal layeron or over the upper and lower polarizer plates and upper/lowersubstrates plus electrodes as well as between electrodes concerned.

FIG. 44 is a characteristic diagram of a simulation result showing atilt angle of liquid crystal molecules within a liquid crystal layeralong with a viewing angle region which becomes greater than or equal to10 in contrast ratio with respect to all directions in a liquid crystaldisplay device of the lateral electric field type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention, still other objects of the present invention, andyet other features of the present invention will become more apparentfrom the explanation presented below with reference to the accompanyingdrawings.

Embodiment 1

An explanation will be given of a color liquid crystal display device ofthe active matrix type to which the present invention is applied. Notethat in the drawings, as will be explained below, those elements thesame function will be identified with the same reference symbol, and anyrepetitive explanation thereof will be omitted.

<<Planar Arrangement of Matrix Section (Pixel Section)>>

FIG. 1 is a plan view showing one pixel along with the nearby portionsof an active-matrix color liquid crystal display device of the presentinvention. (Hatched portions in the drawing indicate a transparentconductive film g2.)

As shown in FIG. 1, each pixel is disposed within a crossover region(within an area as surrounded by four signal lines) of a scan signalline (gate signal line or horizontal signal line) GL and acontra-voltage signal line (counter electrode lead) CL plus twoneighboring image signal lines (drain signal lines or vertical signallines) DL. Each pixel includes a thin-film transistor TFT, a storagecapacitor Cstg, a pixel electrode PX, and a counter electrode CT. Thescan signal line GL and contra-voltage signal line CL are provided as aplurality of lines that extend in the lateral direction as seen in thedrawing and are disposed in the upward/downward direction. A pluralityof image signal lines DL are provided which extend in the up/downdirection and are laid out in the rightward/leftward or lateraldirection. The pixel electrode PX is connected via a source electrodeSD1 to a thin-film transistor TFT, while the counter electrode CT isintegral with the contra-voltage signal line CL.

Two neighboring pixels in the up/down direction along the image signalline DL are arranged as a mirror image of each other so as to overlapeach other when folded along line “A” of FIG. 1. This is for reductionof the resistance of the contra-voltage signal line CL by providing acommon contra-voltage signal line CL between two pixels that neighboreach other in the up/down direction along the image signal line DL tothereby increase the electrode width of the contra-voltage signal lineCL. Whereby, it is easier to sufficiently supply a contra-voltage fromexternal circuitry to the counter electrode CT of each of laterallyadjacent pixels.

The pixel electrode PX and counter electrode CT oppose each other tocontrol the optical state of liquid crystal LC by generating an electricfield between each pixel electrode PX and counter electrode CT tothereby control generating of a display. The pixel electrode PX andcounter electrode CT are designed to have a comb-like shape so that eachbecomes an elongate electrode in the up/down direction of the drawing.

The required number “O” of counter electrodes CT within a single pixel(i.e. the number of comb teeth) is arranged to have a relation of O=P+1relative to the number “P” of pixel electrodes PX (comb teeth number)without failure in any event (in this embodiment, 0=3, P=2). This is inorder to alternately dispose the counter electrodes CT and pixelelectrodes PX while forcing the counter electrode CT to reside adjacentto its associated image signal line DL with no failures. Whereby, it ispossible to allow the counter electrode CT to shield those electric fluxlines extending from the image signal line DL to thereby ensure that anelectric field between the counter electrode CT and pixel electrode PXreceive no influence from an electric field generated from the imagesignal line DL. Since the counter electrode CT is being constantlysupplied with a voltage potential from the outside by a contra-voltagesignal line CL as will be described later, its potential is stabilized.Due to this, even when it is immediately adjacent to its neighboringimage signal line DL, the potential will hardly vary. In addition, withsuch an arrangement, the geometric position of the pixel electrode PXfrom the image signal line DL becomes farther so that the parasiticcapacitance between the pixel electrode PX and image signal line DLdecreases significantly thereby also enabling suppression of anypossible variation of a pixel electrode potential Vs otherwise occurringdue to an image signal voltage. With these arrangements, it is possibleto suppress or reduce cross-talk (i.e., image quality defect called the“longitudinal smear”) occurring in the up/down direction.

The pixel electrode PX and counter electrode CT measure 6 μm inelectrode width. This is to provide a sufficiently larger setup than thethickness, 3.9 μm, of a liquid crystal layer to be described later inorder to apply sufficient electric field to the entire liquid crystallayer with respect to the thickness direction of the liquid crystallayer while at the same time letting it be as fine as possible in orderto increase the aperture ratio. In addition, in order to preventelectrical connection failure or open-circuiting, the electrode width ofimage signal line DL is designed to be wider by little more than that ofthe pixel electrode PX and counter electrode CT-typically, 8 μm. Here,the electrode width of the image signal line DL is set so, that itbecomes less than or equal to twice the electrode width of itsneighboring counter electrode CT. Alternatively, in cases where theelectrode width of image signal line DL has been determined depending onthe productivity of the yield, let the electrode width of the counterelectrode CT neighboring upon the image signal line DL is made less thanor equal to half of the electrode width of the image signal line DL.This is for allowing the counter electrodes CT on the opposite sides toabsorb electric flux lines generated from the image signal line DL. Toabsorb electric flux lines generated from one certain electrode width,it is required to use an electrode having an electrode width that isgreater than or equal to it. Accordingly, since the respective counterelectrodes CT on the opposite sides are expected to absorb electric fluxlines generated from half (4 μm for each) of the electrode of the imagesignal line DL, the electrode width of the counter electrode CTneighboring the image signal line DL is set to ½ or more. This preventsgeneration of crosstalk due to the influence of image signals, inparticular, the up/down-direction (longitudinal crosstalk).

The scan signal line GL is designed to have an electrode width whichsatisfies a resistance value that permits application of a sufficientscanning voltage to a gate electrode GT of a pixel on the distal endside (on the opposite side of as can voltage terminal GTM to bedescribed later). In addition, the contra-voltage signal line CL also isset at an electrode width which satisfies a resistance value thatenables application of a sufficient contra-voltage to the counterelectrode CT of such pixel on the distal end side (on the opposite sideof a common bus line to be discussed later).

On the other hand, the electrode distance or interval between the pixelelectrode PX and counter electrode CT changes depending on a liquidcrystal material used. This is provided, in view of the fact that adifferent liquid crystal material results in a difference in electricfield intensity required for achieving the maximum transmissivity, forsetting the electrode distance depending on the liquid crystal materialin order to insure obtainability of the maximum transmissivity within arange of the maximum amplitude of a signal voltage as set at thewithstanding voltage of an image signal drive circuit (signal-sidedriver) used herein. Supposing that a liquid crystal material to bedescribed later is used, the electrode distance becomes 16 μm.

<<Sectional Arrangement of Matrix Section (Pixel Section)>>

FIG. 2 is a diagram showing a cross-section taken along cut line 3-3 ofFIG. 1; FIG. 3 is a sectional view of a thin-film transistor TFT takenalong line 4-4 of FIG. 1; and, FIG. 4 is a diagram showing incross-section a storage capacitor Cstg taken along line 5-5 of FIG. 1.As shown in FIG. 2 to FIG. 4, a thin-film transistor TFT and storagecapacitor Cstg plus an electrode group are formed on the side of a lowertransparent glass substrate SUB1 with a liquid crystal layer LC beingused as a reference, while a color filter FIL and optical shieldingblack matrix pattern BM are formed on the side of an upper transparentglass substrate SUB2.

In addition, orientation or “alignment” films ORI1, ORI2 for control ofthe initial alignment of liquid crystal are formed on the insidesurfaces (on the liquid crystal LC side) of the transparent glasssubstrates SUB1, SUB2, respectively, while polarizer plates (Cross Nicollayout) are provided on the outside surfaces of respective ones of thetransparent glass substrates SUB1, SUB2 in such a way that thepolarization light axes are at right angles to each other. <<TFTSubstrate>>

A detailed explanation will first be given of an arrangement on the sideof the lower transparent glass substrate SUB1 (TFT substrate).

<<Thin-Film Transistor TFT>>

A thin-film transistor TFT operates in a way such that, upon applicationof a positive bias to its gate electrode GT, the channel resistancebetween the source and drain decreases; and, when letting the bias bezero, the channel resistance increases.

As shown in FIG. 3, the thin-film transistor TFT has a gate electrodeGT, gate insulation film GI, i-type semiconductor layer AS made ofi-type (intrinsic, without doping of any conductivity-type determiningimpurity) amorphous silicon (Si), and a pair of active regionsconsisting of a source electrode SD1 and drain electrode SD2.Additionally, in view of the fact that the source and drain areinherently determinable by a bias polarity therebetween, the polaritythereof will be inverted during operations in the circuitry of thisliquid crystal display device; thus, it should be understood that thesource and drain are interchangeable during operations. However, in theexplanation given below, one of them will be fixedly referred to as the“source” whereas the other will be referred to as the “drain” forpurposes of convenience of discussion only. <<Gate Electrode GT>>

The gate electrode GT is formed so that it is continuous with a scansignal line GL, wherein a partial region of the scan signal line GL isarranged to become the gate electrode GT. The gate electrode GT is thepart that goes beyond the active regions of the thin-film transistorTFT, which is formed to be relatively larger than it to therebycompletely cover the i-type semiconductor layer AS (when looking at fromits lower part). In this way, it is possible to prevent any externallyincoming light and backlight rays from hitting the i-type semiconductorlayer AS, in addition to performing the function of the gate electrodeGT. In this example, the gate electrode GT is formed of a single-layeredconductive film g1. The conductive film g1 is made of an aluminum (Al)film formed by sputtering, for example, on which an anodized film AOF ofAl is provided.

<<Scan Signal Line G1>>

The scan signal line G1 is formed of a conductive film g1. Thisconductive film g1 of the scan signal line G1 is fabricated in the sameprocess step with the conductive film g1 of the gate electrode GT sothat these elements are formed integrally with each other. This scansignal line G1 permits application of a gate voltage Vg from externalcircuitry to the gate electrode GT. In addition, an anodized film AOF ofAl is also provided on the scan signal line G1. Note that a portionwhich intersects with an image signal line DL is narrowed for reductionof the possibility of short-circuiting with the image signal line DL;and, simultaneously, it is Y-bent to resemble a crotch in shape toenable cut-and-separation for electrical disconnection even whenshort-circuiting occurs.

<<Counter Electrode CT>>

The counter electrode CT is constituted from a conductive film g1 of thesame layer as the gate electrode GT and scan signal line G1. Inaddition, an anodized film AOF of Al is also provided on the counterelectrode CT. An arrangement is employed causing a contra-voltage Vcomto be applied to the counter electrode CT. In this embodiment, thevoltage Vcom is set at a selected potential level which is lower by aspecified degree than an intermediate DC voltage potential that isbetween the minimum level of the drive voltage Vdmin and the maximumlevel of the drive voltage Vdmax being applied to the image signal lineDL, which specified degree corresponds to a feed-through voltage ΔVs asgenerated when the thin-film transistor TFT is turned off, although anAC voltage may alternatively be applied thereto in cases where it isrequired that the power supply voltage of an integrated circuit to beused in image signal drive circuitry is half-reduced in potential.

<<Contra-Voltage Signal Line CL>>

The contra-voltage signal line CL is formed of a conductive film g1.This conductive film g1 of the contra-voltage signal line CL isfabricated at the same process step with the forming of the conductivefilm g1 of the gate electrode GT, scan signal line G1 and counterelectrode CT, and also is arranged to be integral with the counterelectrode CT. This contra-voltage signal line CL permits supplement of acontra-voltage Vcom from external circuitry to the counter electrode CT.In addition, an anodized film AOF of Al is provided on thecontra-voltage signal line CL. Note here that a portion which intersectswith the image signal line DL is narrowed, as in the case of the scansignal line G1, in order to decrease the possibility of short-circuitingwith the image signal line DL; and, simultaneously, it is Y-bent toresemble a crotch in shape to permit cut-and-separation for electricaldisconnection even upon occurrence of short-circuiting. <<DielectricFilm GI>>

The dielectric film GI is for use as a gate insulation film for givingan electric field to the semiconductor layer AS along with the gateelectrode GT in the thin-film transistor TFT. The dielectric film GI isformed to overlie the gate electrode GT and scan signal line G1. As thedielectric film GI, a silicon nitride film is chosen which was formed byplasma CVD, for example, to a thickness ranging from 1,200 to 2,700 Á(in this embodiment, 2,400 Á or more or less). The gate insulation filmGI is formed to surround the entire matrix section AR while a peripheralsection was removed thus exposing external connection terminals DTM,GTM. The dielectric film GI also contributes to electrical isolation ofthe image signal line DL with respect to the scan signal line G1 andcontra-voltage signal line CL.

<<i-Type Semiconductor Layer AS>>

The i-type semiconductor layer AS is made of amorphous silicon formed toa thickness of from 200 to 2,200 Á (in this embodiment, approximately2,000 Á). A layer d0 is an N(+) type amorphous silicon semiconductorlayer with phosphorus (P) doped therein for ohmic contact, which is leftonly at a portion where the i-type semiconductor layer AS is present onthe lower side, whereas a conductive layer d1 (d2) exists on the upperside thereof.

The i-type semiconductor layer AS is also provided between both crosspoints (crossover sections) of the image signal line DL with respect tothe scan signal line G1 and contra-voltage signal line CL. The i-typesemiconductor layer AS at these cross points suppresses short-circuitingbetween the scan signal line G1 and contra-voltage signal line CL on onehand and the image signal line DL on the other hand at such crosspoints.

<<Source Electrode SD1, Drain Electrode SD2>>

Each of the source electrode SD1 and drain electrode SD2 is constitutedfrom a conductive film d1 disposed in contact with the N(+) typesemiconductor layer d0 and a conductive film d2 formed thereon.

The conductive film dl may be a chromium (Cr) film that is formed bysputtering to a thickness of from 500 to 1,000 Á (about 600 Á in thisembodiment). In light of the fact that the Cr films increase in stresswhen formed with a large film thickness, this film is to be formedwithin a range that does not exceed a specified film thickness, such asabout 2,000 Á. The Cr film is used in order to provide excellentadhesion with the N(+) type semiconductor layer d0 while at the sametime preventing Al from the conductive film d2 from diffusing into theN(+) semiconductor layer d0 (at the aim of so-called barrier layer). Theconductive film d1 may be made of a high-melting-point metal (Mo, Ti,Ta, W) film or a high-melting-point metal silicide (MbSi₂, TiSi₂, TaSi₂,WSi₂) film in place of the Cr film.

The conductive film d2 is formed by sputtering Al to a thickness of3,000 to 5,000 Á (in this embodiment, about 4,000 Á). The Al film hasless stress than the Cr film and is capable of fabrication to large filmthicknesses; thus, it offers functionality to reduce the resistancevalues of the source electrode SD1 and drain electrode SD2, plus theimage signal line DL, and also to insure a step-like differenceride-over (improve the step coverage) due to the gate electrode GTand/or i-type semiconductor layer AS.

After having patterned the conductive film d1 and conductive film d2 byuse of the same mask pattern, the N(+) type semiconductor layer d0 isremoved using the same mask or alternatively using the conductive filmdl and conductive film d2 as a mask therefor. In other words, residualportions of the N(+) type semiconductor layer d0 on the i-typesemiconductor layer AS, other than the conductive film d1 and conductivefilm d2, are removed in a self-alignment fashion. At this time, sincethe N(+) type semiconductor layer d0 is etched so that the whole partcorresponding to its thickness is removed, the i-type semiconductorlayer AS also will be etched a little on its surface portion—suchetching degree may be controlled by the etching time.

<<Image Signal Line DL>>

The image signal line DL is made up of a second conductive film d2 and athird conductive film d3, which are at the same layer of the sourceelectrode SD1 and drain electrode SD2. In addition, the image signalline DL is formed integrally with the drain electrode SD2.

<<Pixel Electrode PX>>

The pixel electrode PX is formed of a transparent conductive layer g2.This transparent conductive film g2 is made of a transparent conductivefilm (Indium-Tin-oxide ITO: Nesa film) formed by sputtering to athickness of 100 to 2,000 Á (in this embodiment, about 1,400 Á).

The pixel electrode being transparent, as in this embodiment, leads toimprovement of the maximum optical transmissivity when producing a whitedisplay due to rays of light passing through such portion; thus, itbecomes possible to produce a brighter display as compared to the caseof using opaque pixel electrodes. At this time, as will be describedlater, the polarizer plate layout is arranged (in the normally-blackmode) so that liquid crystal molecules retain their initial alignmentstate in the absence of a voltage applied thereto to achieve a blackdisplay under such conditions; and, consequently, even where pixelelectrodes are made transparent, no light rays penetrate such portions,to thereby enable displaying of black with good quality. This in turnmakes it possible to improve the maximum transmissivity while achievingsufficient contrast ratio.

<<Storage Capacitor Cstg>>

The pixel electrode PX is so formed as to overlap the contra-voltagesignal line CL at an opposite end to the end at which it is connected tothe thin-film transistor TFT. As apparent from FIG. 4 also, thisoverlapping results in the formation of a storage capacitor(electrostatic capacitive element) Cstg with the pixel electrode PX asits one electrode PL2 and with the contra-voltage signal line CL as itsremaining electrode PL1. A dielectric film for this storage capacitorCstg is formed of the anodized film AOF and dielectric film GI used asthe gate insulation film of the thin-film transistor TFT.

As shown in FIG. 1, regarding the planar configuration, the storagecapacitor Cstg is formed at a portion where the width of the conductivefilm g1 of contra-voltage signal line CL is widened.

<<Protective Film PSV1>>

A protective film PSV1 is provided on the thin-film transistor TFT. Theprotective film PSV1 is formed to mainly protect the thin-filmtransistor TFT from humidity or the like, and so one that is high intransparency and good in moisture vapor resistance is used. Theprotective film PSV1 is made of a silicon oxide film or silicon nitridefilm fabricated by a plasma CVD apparatus, for example, to a filmthickness of approximately 1 μm.

The protective film PSV1 is formed TO entirely surround the matrixsection AR, whose peripheral section has been removed to expose theexternal connection terminals DTM, GTM. With regard to the relative ofthicknesses of the protective film PSV1 and gate insulation film GI, theformer is made thick in light of the protection effect, whereas thelatter is made thinner in view of the mutual conductance of thetransistors involved. Accordingly, the protective film PSV1 with a highprotecting effect is formed so that it is larger than the gateinsulation film GI to ensure that its periphery may also protect over anextended area that is as wide as possible.

<<Color Filter Substrate>>

Next, turning back to FIG. 1 and FIG. 2, a detailed explanation will begiven of an arrangement of the upper transparent glass substrate SUB2(color filter substrate).

<<Optical Shield Film BM>>

An optical shield film BM (so-called black matrix) is formed on the sideof the upper transparent glass substrate SUB2 for preventing reductionof the contrast ratio or the like which otherwise occurs due to outwardemission of transmission light from unnecessary gaps (gaps other thanthat between the pixel electrode PX and counter electrode CT) toward thedisplay plane side. The optical shield film BM also functions to preventrays of either external light or backlight from falling onto the i-typesemiconductor layer AS. More specifically, the i-type semiconductorlayer AS of the thin-film transistor TFT is sandwiched by the opticalshield film BM and the gate electrode GT of larger size, which are atthe upper and lower locations, to thereby eliminate hitting of externalincoming natural light and backlight rays.

The contour line of a closed polygon of the optical shield film BM shownin FIG. 1 indicates an opening within which the optical shield film BMis not formed. This contour line pattern is a mere example, and in thecase of enlarging the opening portion, it may be replaced with anoptical shield film BM1 as shown by dotted lines in FIG. 1. Although theexpanded region in FIG. 1 can experience a disturbance of the electricfield direction, a display at such portion is in one-to-onecorrespondence to image information within pixels so that black isobtained in the case of black and white is obtained for white;accordingly, it can be utilized as part of such display. In addition,the boundary line in the up/down direction of the drawing is determinedby the accuracy of positional alignment between the upper and lowersubstrates; and, in case the alignment accuracy is better than theelectrode width of the counter electrode CT that neighbors the imagesignal line DL, it is possible to further enlarge the opening section bysetting it between the widths of the counter electrode.

The optical shield film BM has a shielding effect with respect to light,and is made of a highly insulative film for elimination of any badinfluence on an electric field between the pixel electrode PX andcounter electrode CT in this embodiment, it is made of a resist materialwith black pigment mixed thereinto and formed to a thickness of 1.2 μm,more or less.

The optical shield film BM is formed into a net mesh or lattice-likeshape around each pixel so that this lattice is used for partitioningthe effective display area of a single pixel. Thus, the contour line ofeach pixel is made clear by the optical shield film BM. In other words,the optical shield film BM functions as a black matrix while at the sametime functioning to optically shield the i-type semiconductor layer AS.

The optical shield film BM is also formed at the periphery to have awindow frame-like shape, whose pattern is formed in a way continuouswith a pattern of the matrix section shown in FIG. 1 with a plurality ofdot-like openings provided therein. The optical shield film BM at theperiphery is extended toward the outside of a seal section SL therebypreventing leakage light, such as reflection light due to practicalmount equipment, such as personal computers, from entering or “invading”the matrix section. On the other hand, this optical shield film BM islimited in location so that it resides within an inside area smaller byabout 0.3 to 1.0 mm than the edge of the substrate SUB2, and also isformed excluding cutaway regions of the substrate SUB2.

<<Color Filter FIL>>

A color filter FIL is formed to have a stripe shape with red, green andblue being repeated at positions that correspond to pixels. The colorfilter FIL is formed to overlap edge portions of the optical shield filmBM.

The color filter FIL can be formed in a way which follows. Firstly, adyeing base material, such as acrylic resin, is formed on the surface ofthe upper transparent glass substrate SUB2; and then, usingphotolithography techniques the dyeing base material other thanred-filter formation regions, is removed. Thereafter, the dyeing base isdyed with red pigment; and then, fixation processing is performed toform a red filter R. Next, similar processes are effected tosequentially form a green filter G and a blue filter B.

<<Overcoat Film OC>>

An overcoat film OC is provided for elimination of leakage of dye of thecolor filter FIL into the liquid crystal Lc and also for planarizationof the step-like surface configuration due to the color filter FIL andoptical shield film BM. The overcoat film OC is formed of a transparentresin material, such as, for example, acrylic resin, epoxy resin or thelike.

<<Liquid Crystal Layer and Polarizer Plate>>

An explanation will next be given of a liquid crystal layer andalignment films as well as polarizer plates and the like.

<<Liquid Crystal Layer>>

A nematic liquid crystal material is used as the liquid crystal materialLC, which is positive in dielectric anisotropy Δ∈ and measures 13.2 invalue, while its refractive anisotropy Δn is 0.081 (589 nm at 20° C.).The liquid crystal layer is 3.9 μm in thickness and 0.316 in retardationΔn·d. Due to the value setup of this retardation Δn·d, the maximumtransmissivity can be obtained in combination with an alignment film(s)and polarizer plate(s) to be described later when letting liquid crystalmolecules rotate in the direction of an electric field by 45° from therubbing direction, thereby making it possible to obtain transmittedlight with little or no waveform dependency within the range of visiblelight. Additionally, the thickness (gap) of the liquid crystal layer iscontrolled by polymer beads.

It should be noted that the liquid crystal material LC should not belimited to the one suggested above and that the dielectric anisotropy Δ∈may alternatively be negative in polarity. In addition, setting thedielectric anisotropy Δ∈ at greater values enables the drive voltage todecrease in potential. In addition, reducing the refractive anisotropyΔn makes it possible to increase the thickness (gap) of the liquidcrystal layer, which in turn enables the liquid crystal sealing time tobe shortened while reducing gap deviation.

Further, investigating the relation of the solid-state properties of theliquid crystal material versus the intensity of transmitted light atpart of the transparent conductive film corresponding to either thecounter electrode or the pixel electrode, it has been found that thisrelationship significantly depends on the twist elastic modulus K2 ofthe liquid crystal material used. This is because attenuation ofin-plane twist deformation at the upper part of the electrode of thetransparent conductive film due to a lateral electric field leading totransmission of light at an opening between electrodes takes place atits inherent curvature ratio in accordance with the twist elasticmodulus K2 of the liquid crystal material. Thus, in order to improve thebrightness or luminance of the entire opening, including the electrodeof this transparent conductive film, by increasing the lighttransmission at the electrode portion of the transparent conductivefilm, a certain liquid crystal material having a lower twist elasticmodulus K2 is employed for reduction of the attenuation curvature ratio.The effect of the twist elastic modulus K2 will be further described inan embodiment 11.

In this embodiment 1, the twist elastic modulus K2 is set at 5.1×10⁻¹² N(Newton) at room temperature.

Note that one typical method of measurement of the twist elastic modulusK2 has been disclosed in, for example, “LIQUID CRYSTALS Fundamentals,”by Kohji Okano and Shunsuke Kobayashi at pp. 216-220 (Baifu-Kan, 1985)cited herein as a reference, which teaches that the modulus isobtainable through measurement of the threshold voltage of a liquidcrystal cell that has twisted.

<<Alignment Film>>

Polyimide is used as the alignment films ORI, and the rubbing directionsare parallel to each other for the upper and lower substrates whilesetting the initial alignment angle φLC at 75°, which angle is definedbetween the initial alignment direction RDR and the applied electricfield direction EDR (Ex). Its relation is shown in FIG. 19.

Additionally, the initial alignment angle φLC defined between theinitial alignment direction RDR and the applied electric field directionEDR is such that when the dielectric anisotropy Δ∈ of the liquid crystalmaterial is positive in polarity, it must be greater than or equal to45° C. and yet less than 90° C.; whereas, if dielectric anisotropy Δ∈ isnegative, then it must exceed 0° and remains below 45°.

Further, in this embodiment, letting the rubbing directions be parallelto each other with respect to alignment films ORI1, ORI2 causes theinitial pre-tilt angle of liquid crystal molecules at the upper andlower interfaces of the liquid crystal layer, contributing to displaybetween electrodes and over electrodes, to be in the splay state,thereby allowing such liquid crystal molecules to exhibit an effect ofmutually compensating for optical characteristics resulting inachievement of wide viewing-angle characteristics.

Alternatively, letting the rubbing directions be antiparallel to eachother with respect to the alignment films ORI1 ORI2 causes the initialpretilt angle of liquid crystal molecules at the upper and lowerinterfaces of the liquid crystal layer to become in the parallel stateresulting in an increase in average tilt angle inside of the liquidcrystal layer. In such case, however, setting the pretilt angle at orbelow 10 degrees enables accomplishment of similar effects of thepresent invention.

<<Polarizer Plate>>

As the polarizer plates POL, G1220DU manufactured by Nitto Denko-Sha isused, wherein the polarized light transmission axis MAX1 of a lower sidepolarizer plate POL1 is rendered identical to the rubbing direction RDR;whereas, the polarized light transmission axis MAX2 of an upper sidepolarizer plate POL2 is disposed at right angles thereto. The relationthereof is shown in FIG. 19. Thus, it becomes possible to obtain anormally-close characteristic which lets the transmissivity increasewith an increase in a voltage being applied to the pixel in accordancewith the present invention (voltage between the pixel electrode PX andcounter electrode CT), while enabling achievement of a black display ofgood quality when applying no voltages thereto.

In addition, the polarizer plate POL2 per se is provided with atransparent conductive film that is formed on its entire surface for thepurpose of eliminating the bad influence of static electricity from theoutside to thereby reduce the specific resistance thereof. Thistransparent conductive film may alternatively be formed between theupper substrate SUB2 and the upper polarizer plate POL2. <<Arrangementof Matrix Periphery>>

FIG. 5 is a diagram showing a plan view of a main part at the peripheryof the matrix (AR) of the display panel PNL including the upper andlower glass substrates SUB1, SUB2. FIG. 6 is a diagram showing, on itsleft side, a cross-section near an external connection terminal GTM towhich scan circuitry is to be connected, and also showing on its rightside a cross-section near a seal section at which no external connectionterminals are present.

With this panel structure, a glass sheet is cut into pieces through aseries of process steps in such a way that, if it is small in size, thena single glass substrate is used for simultaneous fabrication of aplurality of devices thereon and then subject to subdivision by cuttingprocesses in order to improve the throughput, or alternatively, if it isof large size, then a glass substrate of preselected size that isstandardized for any type of product is processed and then made smallerinto a required size adaptable for use with each product type in orderto attain common usability of a manufacturing facility. FIG. 5 and FIG.6 show an example of the latter case, wherein both FIG. 5 and FIG. 6represent a structure obtained after having cut the upper and lowersubstrates SUB1, SUB2, and wherein LN denotes an edge before cutting. Ineither case, in the completed state, those portions (upper side andlower side in the drawing) at which the external connection terminalgroup Tg, Td and terminal COT (suffix eliminated) exist are limited sothat the size of the upper side substrate SUB2 is inside of the lowerside substrate SUB1 to thereby expose them. The terminal groups Tg, Tdare each a bundle of plural lines including scan circuit connectionterminals GTM and image signal circuit connect terminals DTM along withtheir extension lead section, as will be described later, in units oftape carrier packages TCP (FIG. 16, FIG. 17) each having an integratedcircuit chip CHI mounted thereon. An extension lead from a matrixsection of each group up to an external connection terminal section isslanted or tilted as it comes closer to both ends. This is in order toalign the terminals DTM, GTM of the display panel PNL with the layoutpitch of packages TCP and also with the connection terminal pitch ateach package TCP. In addition, the counter electrode terminal CTM is aterminal for use in supplying a contra-voltage from external circuitryto the counter electrode CT. The contra-voltage signal line CL of thematrix section is drawn out toward the opposite side (right side in thedrawing) of I the scan circuit terminal GTM while bundling togetherrespective contra-voltage signal lines by a common bus line CB forconnection to the counter electrode terminal CTM.

A seal pattern SL is formed between the transparent glass substratesSUB1, SUB2 along the edges thereof except for a liquid crystal sealingport INJ to permit sealing of the liquid crystal LC. The seal materialis made of epoxy resin, for example.

Layers of alignment films ORI1, ORI2 are formed inside of the sealpattern SL. The polarizer plates POL1, POL2 are arranged on outersurfaces of the lower-part transparent glass substrate SUB1 andupper-part transparent glass substrate SUB2, respectively. The liquidcrystal LC is sealed in a region that is partitioned by the seal patternSL between the lower-part alignment film ORI1 and upper-part alignmentfilm ORI2 for setting the direction of liquid crystal molecules. Thelower-part alignment film ORI1 is formed at the upper part of theprotective film PSV1 on the side of the lower-part transparent glasssubstrate SUB1.

This liquid crystal display device is assembled by laminating variouslayers independently on the side of the lower-part transparent glasssubstrate SUB1 and on the side of upper-part transparent glass substrateSUB2, forming the seal pattern SL on the substrate SUB2 side,overlapping the lower-part transparent glass substrate SUB1 andupper-part transparent glass substrate SUB2, injecting the liquidcrystal LC from an opening INJ of the seal material SL, sealing theinjection port INJ by epoxy resin or the like, and cutting the upper andlower substrates.

<<Gate Terminal>>

FIG. 7A is a plan view showing a connection structure extending from thedisplay matrix's scan signal line G1 up to its external connectionterminal GTM; and FIG. 7B shows a cross-section at line B-B of FIG. 7A.Note that the same drawing corresponds to the FIG. 5 right centervicinity, wherein the hatched part is represented by a straight lineshape for purposes of convenience.

“AO” is a boundary line of photoresist direct drawing—in other words, aphotoresist pattern of selective anodization. Accordingly, thisphotoresist is to be removed after anodization, and the pattern AO shownin the drawing is not left as a complete product; however, its trace isleft because the oxide film AOF is selectively formed at the gate leadG1 as shown in the sectional drawing. In the plan view diagram, the leftside with the photoresist's boundary AO serving as a reference is theregion that is covered with a resist and is not subject to anodization;and the ride side is the region that is exposed from the resist and isanodized. An Al layer g1 anodized has a surface on which the oxide Al₂O₃film AOF is formed, wherein the lower conductor part decreases involume. Of course, the anodization is performed after setting of anappropriate time and voltage to ensure that its conductor part remains.

Although in the drawing the Al layer g1 is hatched for clarity purposes,a non-anodized region is patterned into a comb-like shape. This is doneto achieve suppression or minimization of the possibility ofshort-circuiting and/or any possible sacrifice of dielectric constant,while simultaneously preventing generation of whiskers otherwiseoccurring when the Al layer is large in width, by narrowing the width ofevery single one for provision of an arrangement of such plurality oflines bundled together.

The gate terminal GTM is comprised of the Al layer g1 and a further atransparent conductive layer g2 that is provided for protecting thesurface thereof and for improving the reliability of connection with aTCP (Tape Carrier Package). This transparent conductive film g2 makesuse of a transparent conductive film ITO that was formed at the sameprocess step with the forming of the pixel electrode PX. in addition,the Al layer g1 and the conductive layers d1 and d2 formed on itslateral side are provided in an attempt to reduce the connectionresistance by connecting a connectivity-excellent Cr layer d1 to boththe Al layer and the transparent conductive layer g2 in order tocompensate for any connection failures between the Al layer and thetransparent conductive layer g2; and the conductive layer d2 is left dueto the fact that it is formed using the same mask as that of theconductive layer d1.

In the plan view diagram, the gate insulation film GI is formed on theright side relative to its boundary line while the protective film PSV1is also formed on the right side of its boundary, wherein the terminalsection GTM placed on the left edge is arranged to be exposed and enableelectrical contact with external circuitry. Although in the drawing onlyone pair of the gate line G1 and gate terminal is depicted, the actualimplementation is such that a plurality of such lines are laid out inthe up/down direction as shown in FIGS. 7A, 7B to constitute theterminal group Tg (FIG. 5), wherein the left end of the gate terminal isextended beyond the cutting region of the substrate to beshort-circuited by a lead SHg (not shown) during the manufacturingprocesses. The provision of such a short-circuiting line SHg during themanufacturing processes is useful for power feed at the step ofanodization and also for electrostatic breakdown during rubbing of thealignment film ORI1.

<<Drain Terminal DTM>>

FIG. 8A shows a plan view diagram showing connection from the imagesignal line DL to its external connection terminal DTM; and FIG. 8Bshows a cross-section at line B-B of FIG. 8A. Note that the same drawingcorresponds to the FIG. 5 upper right vicinity, and that although thedirection of the drawing is changed for convenience purposes, the rightend direction corresponds to the upper end section of the substrateSUB1.

“TSTd” is a test terminal to which external circuitry is not connectedand which is widened to have a width greater than that of the leadsection to permit contacting of a probe needle or the like. Similarly,the drain terminal DTM also is widened to have a width greater than thatof the lead portion to enable connection with external circuitry.External connection drain terminals DTM are laid out in the up/downdirection; and, as shown in FIG. 5, the drain terminals DTM constitutethe terminal group Td (suffix eliminated) and are designed to furtherextend beyond the cut line of the substrate SUB1, all of which areshort-circuited to one another by more than one lead SHd (not shown)during the manufacturing processes for prevention of electrostaticbreakdown. As shown in FIG. 8A, test terminals TSTD are formed atalternate ones of the image signal lines DL.

The drain connection terminal DTM is formed of a single transparentconductive layer g2 and is connected to an image signal line DL at acertain part from which the gate insulation film GI is removed. Thistransparent conductive film g2 makes use of a transparent conductivefilm ITO that was formed at the same process step with the forming ofpixel electrodes PX as in the case of the gate terminal GTM. Asemiconductor layer AS formed on the end portion of the gate insulationfilm GI is provided for use in etching the edge of gate insulation filmGI into a taper shape. Obviously, on or over the drain terminal DTM, theprotective film PSV1 has been removed in order to perform connectionwith external circuitry.

An extension lead from the matrix section up to the drain terminalsection DTM is such that those layers d1, d2 at the same level as theimage signal line DL are arranged at a midway portion of the protectivefilm PSV1 and are connected with the transparent conductive film g2within the protective film PSV1. This has the objective of obtainingmaximized protection of the easily electrolytically corrodible Al layerd2 by use of the protective film PSV1 and/or seal pattern SL.

<<Counter Electrode Terminal CTM>>

FIG. 9A shows a plan view diagram showing connection from thecontra-voltage signal CL up to its external connection terminal CTM; andFIG. 9B shows a cross-section at line B-B of FIG. 9A. Note that thedrawing corresponds to the upper left part of FIG. 5 or therearound.

Respective contra-voltage signal lines CL are bundled by a common busline CB to be drawn out toward the counter electrode terminal CTM. Thecommon bus line CB is structured from a lamination of a conductive layerd1 and conductive layer d2 on the conductive layer g1. This is in orderto reduce the resistivity of the common bus line CB to thereby ensurethat a contra-voltage is sufficiently supplied from external circuitryto each contra-voltage signal line CL. In the structure shown herein, afeature thereof lies in the ability to reduce the resistance of thecommon bus line without newly loading any specific conductive layers.The conductive layer g1 of the common bus line CB is eliminated fromanodization to insure electrical connection with the conductive layersd1 and conductive layer d2. Additionally, it is exposed from the gateinsulation film GI also.

The counter electrode terminal CTM is structured from the conductivelayer g1 and the transparent conductive layer g2 as laminated thereon.This transparent conductive film g2 employs a transparent conductivefilm ITO that was formed at the same process step with the forming ofpixel electrodes PX, as in the other terminals. The conductive layer g1is covered with the transparent conductive layer g2 that is excellent indurability so that the transparent conductive layer g2 will protect itssurface for elimination of electrolytic corrosion.

<<Display Device Overall Equivalent Circuit>>

An equivalent circuit of the display matrix section and its peripheralcircuit's connection diagram are shown in FIG. 10. While this drawing isa circuit diagram, it has been illustrated in a way corresponding to theactual geometric layout. “AR” is a matrix array with a plurality ofpixels laid out in a two-dimensional fashion.

In the drawing, “X” denotes image signal lines DL and has suffices “G”,“B”, and “R” appended thereto, which stand for green, blue and redpixels, respectively. “Y” denotes scanning signal lines G1 with suffices1, 2, 3, . . . , “end”, which denotes the order of sequence of the scantiming.

The scan signal lines Y (suffix eliminated) are connected to a verticalscan circuit V, while the image signal lines X (suffix omitted) arecoupled to an image signal driving circuit H.

“SUP” denotes circuitry including a power supply circuit for obtaining aplurality of stabilized voltage sources voltage-divided from a singlevoltage source along with a circuit or circuits for conversion ofinformation for a CRT (cathode-ray tube) from a host (upper-level or“supervisory” arithmetic processing device) into information for usewith a TFT liquid crystal display device.

<<Driving Method>>

Several drive waveforms of the liquid crystal display device of thepresent invention are shown in FIG. 11.

As in the embodiment 1 the contra-voltage signal line CL is made of theconductive film g1 of a low-resistivity metal such as aluminum, and theload impedance is less, thereby reducing waveform deformation of acontra-voltage. Due to this, it becomes possible to employ an AC voltageas the contra-voltage, which in turn advantageously reduces the signalline voltage.

More specifically, the contra-voltage is designed to have a rectangularAC waveform with binary values of Vdh and Vcl, while letting anon-selected voltage of scan signals Vg(i−1), Vg(i) change betweenbinary values Vglh and Vgll in synchronism therewith once per scanperiod. The amplitude value of such contra-voltage is the same as theamplitude of the non-select voltage. An image signal voltage is thevoltage equivalent to a desired voltage being applied to the liquidcrystal layer from which % of the amplitude of the contra-voltage issubtracted.

While the contra-voltage may be a DC voltage, use of an AC voltage makesit possible to reduce the maximum amplitude of the image signal voltage,which in turn enables employment of a low-withstanding-voltage circuitfor the image signal drive circuit (signal-side driver). In embodiments2 and 3 to be described later, since the contra-voltage signal line CLis formed of a transparent conductive film g2, the resistance becomescomparatively high; and, in such cases, the contra-voltage is preferablyof the DC scheme.

<<How Storage Capacitor Cstg Works>>

The storage capacitor Cstg is provided for accumulating therein imageinformation written into a pixel (after the thin-film transistor TFT wasturned off). In the scheme used by the present invention for applying anelectric field in a direction parallel to the substrate surface, unlikethe scheme for applying an electric field in a vertical directionrelative to the substrate surface, the storage capacitor Cstg isincapable of accumulating image information in a pixel due to the factthat little or no capacitance (known as liquid crystal Capacitance) isformed by a pixel electrode and its counter electrode. Accordingly, withthe when applying an electric field in a direction parallel to thesubstrate surface, the provision of a storage capacitor Cstg becomes anessential consideration.

In addition, when the thin-film transistor TFT performs switching, thestorage capacitor Cstg also functions to reduce the influence of a gatepotential variation Avg with respect to a pixel electrode potential Vs.This may be represented by:ΔVs={Cgs/(Cgs+Cstg+Cpix)}×ΔVg,where, Cgs is the parasitic capacitance as formed between the gateelectrode GT and the source electrode SD1 of a thin-film transistor TFT,Cpix is the capacitance formed between a pixel electrode PX and itscounter electrode CT, and ΔVs is a variation component of the pixelelectrode potential due to ΔVg, also known as a feed-through voltage.While this variation component ΔVs becomes the cause of a DC componentbeing applied to the liquid crystal LC, it is possible to decrease itsvalue by increasing the storage capacitance Cstg. Reduction of DCcomponents being applied to the liquid crystal LC leads to improvementof the lifetime of the liquid crystal LC while at the same time enablingsuppression of the so-called “burn-in” or “seizing” phenomenon in whicha prior image is retained after switching of a liquid crystal displayscreen.

As previously discussed, as the gate electrode GT is enlarged enough tocompletely cover the i-type semiconductor layer AS, an overlap area withthe source electrode SD1 and drain electrode SD2 increases accordingly,resulting in an increase in parasitic capacitance Cgs, which in turnleads to creation of an adverse effect that the pixel electrodepotential Vs can readily receive the influence of the gate (scan) signalVg. However, provision of the storage capacitor Cstg makes it possibleto avoid this problem.

<<Manufacturing Method>>

An explanation will next be given of a method of manufacturing thesubstrate SUB1 of the above-mentioned liquid crystal display device withreference to FIG. 12 to FIG. 14. Note that in these drawings, thecharacters centrally indicated therein are process names abbreviated,wherein a flow of fabrication process steps is shown while indicating onits left side a cross-section of the thin-film transistor TFT part shownin FIG. 3 along with a cross-section at or near the gate terminal shownin FIG. 7 on the right side. Except for a process step B and step D,step A-step I are partitioned in a way corresponding to eachphotographic processing, wherein any one of such process steps indicatesthe stage where the fabrication processing after the photographicprocess has been completed with a photoresist removed already. Note thatthe term “photographic processing” as used herein refers to a series ofoperations from deposition of a photoresist through selective exposureusing a mask up to development thereof, and any repetitive explanationthereof will be eliminated. An explanation will be given in accordancewith the process steps thus partitioned.

Step A, FIG. 12

A conductive film g1 that is made of Al—Pd, Al—Si, Al—Ta, Al—Ti—Ta, orthe like, is provided by sputtering on the lower transparent glasssubstrate SUB1 comprised of AN635 glass (Trade Name), to a thickness of3,000 Á. After having effected photographic processing, the conductivefilm g1 is selectively etched by use of a mixed acid liquid consistingof phosphoric acid and nitric acid plus glacial acetic acid. Thus, gateelectrodes GT, scan signal lines G1, counter electrodes CT,contra-voltage signal lines CL, electrodes PL1, gate terminals GTM,first conductive layer of common bus lines CB, first conductive layer ofcounter electrode terminals CTM, anodized bus lines SHg (not depicted)for connection of the gate terminals GTM, and anodized pads (notdepicted) as connected to the anodized bus lines SHg are formed.

Step B, FIG. 12

After having formed an anodization mask AO due to direct painting, thesubstrate SUB1 is put into an anodization liquid that is comprised of aliquid of 3%-tartaric acid adjusted to a PH of 6.25±0.05 by ammonia,which liquid is in turn diluted to 1:9 using ethylene glycol liquid, tothereby perform an adjustment so that the formation current density isat 0.5 mA/cm² (constant current formation). Next, anodization isperformed until it reaches the target formation voltage of 125V asrequired for achieving a predetermined Al₂O₃ film thickness. Thereafter,it is desirable that this condition be retained several tens of minutes(constant voltage formation). This is important for achieving a uniformAl₂O₃ film. Then, the conductive film g1 is anodized thereby forming ananodized film AOF, 1,800 Á thick, on the gate electrodes GT, scan signallines G1, counter electrodes CT, contra-voltage signal lines CL andelectrodes PL1.

Step C, FIG. 12

After having introduced into the plasma CVD apparatus an ammonia gas andshiran gas plus nitrogen gas to provide a Si nitride film of 2,200 Áthick, a shiran gas and hydrogen gas are introduced into the plasma CVDapparatus to provide an i-type amorphous Si film of 2.0 thick; andthereafter, a hydrogen gas and phosphine gas are introduced into theplasma CVD apparatus to thereby provide an N(+) type amorphous Si filmto a thickness of 300 Á.

Step D, FIG. 13

After having effected photographic processing, the N(+) type amorphousSi film and i-type amorphous Si film are selectively etched by using SF₆and CCl₄ as dry etching gases to thereby form more than one island ofi-type semiconductor layer AS.

Step E, FIG. 13

After the photographic processing, the Si nitride film is selectivelyetched by use of SF₆ as a dry etching gas.

Step F, FIG. 13

A transparent conductive film g2 made of an ITO film of 1,400 Áthickness is provided by sputtering. After photographic processing, thetransparent conductive film g2 is selectively etched by using as etchingliquid a mixed acid liquid of hydrochloric acid and nitric acid, therebyforming the uppermost layer of gate terminals GTM along with the secondconductive layer of drain terminals DTM and counter electrode terminalsCTM.

Step G, FIG. 14

A conductive film d1 made of Cr is provided by sputtering to a thicknessof 600 Á; and a conductive film d2, 4,000 Á thick, made of Al—Pd, Al—Si,Al—Ti—Ta or the like is also provided by sputtering. After photographicprocessing, the same liquid as that used at the step B is used to etchthe conductive film d2; then, the same liquid as that at the step A isused to etch the conductive film d1 to thereby form the secondconductive layer, third conductive layer of image signal lines DL,source electrodes SD1, drain electrodes SD2, pixel electrodes PX,electrodes PL2 and common bus lines CB, along with more than one busline SHd (not shown) for short-circuiting of the drain terminals DTM.Next, CCl₄ and SF₆ are introduced into the dry etching apparatus to etchthe N(+) type amorphous Si film for selective removal of an N(+) typesemiconductor layer d0 between the source and drain.

Step H, FIG. 14

An ammonia gas and shiran gas plus nitrogen gas are introduced into theplasma CVD apparatus to provide a 1 μm-thick Si nitride film. Afterphotographic processing, a protective film PSV1 is formed by selectivelyetching the Si nitride film by photolithography techniques using SF₆ asa dry etching gas.

<<Display Panel PNL & Drive Circuit Board PCB1>>

FIG. 15 is an upper-side plan-view showing the state in which thedisplay panel PNL shown in FIG. 5 and the like is connected with animage signal drive circuit H and vertical scanning circuit V.

CH1 denotes driver IC chips for use in driving the display panel PNL(lower five ones are driver IC chips on the vertical scan circuit side,whereas every left-side group of ten are driver IC chips on the imagesignal drive circuit side). TCP denotes a tape carrier package withdriver IC chips CHI mounted thereon by tape-automated bonding (TAB)methods as will be described later with reference to FIG. 16 and FIG.17; and PCB1 is a driver circuit board with the TCP and capacitorsmounted thereon, which is divided into two portions, one of which is forthe image signal driver circuit and the other of which is for the scansignal driver circuit. FGP denotes frame ground pads to whichspring-like fragments provided by cutting in a shield case SHD are to besoldered. FC denotes flat cables for electrical connection of thelower-side driver circuit board PCB1 and left-side driver circuit boardPCB1. As shown in the drawing, the flat cables FC being employed arethose which are each comprised of a plurality of lead lines (each madeof Sn-metallized phosphor bronze) that are sandwiched between andsupported by a stripe-shaped polyethylene layer and polyvinyl alcohollayer.

<<Connection Structure of TCP>>

FIG. 16 is a diagram showing a sectional structure of the tape carrierpackage TCP wherein the integrated circuit chips CHI constituting thescan signal driver circuit V and image signal driver circuit H aremounted on a flexible printed circuit board; and FIG. 17 is a main-partsectional diagram showing the state of connecting them to the scansignal circuit terminals GTM of the liquid crystal display panel in thisembodiment.

In the drawings, TTB denotes an input terminal/lead section ofintegrated circuit CHI, and TTM denotes an output terminal/lead sectionof integrated circuit CHI—for example, these are made of Cu, and bondingpads PAD of integrated circuits CHI are connected by so-called face-downbonding methods to respective inside distal end portions (generallycalled “inner leads”). Outside distal end portions of terminals TTB, TTM(generally called “outer leads”) correspond to inputs and outputs ofsemiconductor integrated circuit chips CHI, respectively, which areconnected by soldering or the like to CRT/TFT converter circuit/powersupply circuit SUP and are connected by an anisotropic conductive filmACF to the liquid crystal display panel PNL. The package TCP has itsdistal end portion which is connected to the panel in such a way as tocover the protective film PSV1 that exposes the connection terminals GTMon the panel PNL side; thus, the external connection terminals GTM (DTM)are covered with at least one of the protective film PSV1 and thepackage TCP to thereby increase durability against electrolyticcorrosion.

BF1 is a base film made of polyimide or the like; and SRS is a solderresist film for masking to prevent a solder from adhering to unwantedextra portions during the soldering processes. A gap space between theupper and lower glass substrates outside of the seal pattern SL isprotected by an epoxy resin EPX after having effected cleaningtreatment, wherein a silicon resin SIL is further filled between thepackage TCP and the upper-side substrate SUB2 for multiplexing ofprotection.

<<Driver Circuit Board PCB2>>

A driver circuit board PCB2 is designed to have mounted thereonelectronics parts or components including ICs and capacitors as well asresistors. Also mounted on this driver circuit board PCB2 are a powersupply circuit for obtaining a plurality of stabilized voltage sourcesvoltage-divided from a single voltage source along with circuitry SUPthat includes a circuit for converting information for a CRT(cathode-ray tube) from the host (upper-level arithmetic processingdevice) into information for use with the TFT liquid crystal displaydevice. CJ denotes a connector connect section to which a connector, notshown, to be connected to the outside will be connected.

The driver circuit board PCB1 and driver circuit board PCB2 areelectrically connected together by one or more flat cables FC.

<<Overall Arrangement of Liquid Crystal Display Module>>

FIG. 18 is an exploded perspective view showing respective components orelements of a liquid crystal display module MDL.

SHD is a frame-like shield casing (metal frame) formed of a metal plate;LCW is its display window; PNL, a liquid crystal display panel; SPB, anoptical diffusion plate; LCB, a photoconductor RM, a reflector plate;BL, a backlight fluorescent tube; LCA, a backlight casing, whereinrespective members are laminated or stacked in the layout relationshipshown in the drawing for assembly of the module MDL.

The module MDL is arranged so that the entire device is fixed by morethan one nail-and-hook combination as provided at the shield case SHD.

The backlight case LCA has a shape that permits internal accommodationof the backlight fluorescent tube BL and optical diffusion plate SPBplus photoconductor LCB as well as reflector plate RM, whereby thephotoconductor LCB and reflector plate RM plus optical diffusion plateSPB convert the light from the backlight fluorescent tube BL as disposedalong the lateral plane of the photoconductor LCB into uniform orcoherent backlight on the display plane for outward projection towardthe liquid crystal display panel PNL.

The backlight fluorescent tube BL is operatively associated with aninverter circuit board PCB3 connected thereto thus providing a powersupply of the backlight fluorescent tube BL.

As apparent from the foregoing, in this embodiment, making the pixelelectrodes transparent enables the maximum optical transmissivity toimprove by approximately 30% (31.8% in this embodiment) during whitedisplaying.

More practically, with this embodiment, the optical transmissivity wasimproved from approximately 3.8% obtained when employing opaque pixelelectrodes up to about 5.0% as a result of employment of transparentpixel electrodes.

Additionally, it becomes possible to simultaneously fabricate the ITOfilm for improvement of the reliability of the elements concerned, whichin turn makes it possible to achieve both increased reliability andproductivity at the same time.

Embodiment 2

This embodiment is the same as the embodiment 1 stated above except forthe following points. A plan view diagram of pixels is shown in FIG. 20.Hatched portions in the drawing designate a transparent conductive filmg2.

<<Pixel Electrode PX>>

In this embodiment the pixel electrode PX is constituted from a secondconductive film d2 that is the same in layer as the source electrode SD1and drain electrode SD2, and a third conductive layer d3. In addition,the pixel electrode PX is formed integrally with the source electrodeSD1.

<<Counter Electrode CT>>

In this embodiment the counter electrode CT is comprised of atransparent conductive film g2. This transparent conductive film g2 ismade of a sputtering-fabricated transparent conductive film(Indium-Tin-Oxide ITO: Nesa film) as in the embodiment 1, and is formedto a thickness ranging from 100 to 2,000 Á (in this embodiment, a filmthickness of about 1,400 Á).

<<Contra-Voltage Signal Line CL>>

The contra-voltage signal line CL is formed by a transparent conductivefilm g2, and is designed so that it is integral with the counterelectrode CT.

<<Gate Terminal Section>>

In this embodiment, the transparent conductive layer g2 for protectionof the surface of an Al layer g1 of gate terminal GTM, while improvingthe reliability of connection with the TCP (Tape Carrier Package, isformed at the same step with the forming of counter electrode CT. Thearrangement is identically the same as that of embodiment 1, and is asshown in FIGS. 7A, 7B.

<<Drain Terminal DTM>>

In this, embodiment the transparent conductive layer g2 of drainconnection terminals DTM is made of a transparent conductive film ITOthat was formed simultaneously during formation of counter electrodesCT, as in the case of the gate terminals GTM. While the arrangement isslightly different from embodiment 1 in the up/down relationship oflayers involved, such difference is not essential and for this reasonits illustration is omitted herein.

<<Counter Electrode Terminal CTM>>

The transparent conductive layer g2 overlying the conductive layer g1 ofcounter electrode terminals CTM is comprised of a transparent conductivefilm ITO that was formed at the same process step with the forming ofcounter electrodes CT, in a way similar to that of other terminals. Thearrangement is no longer dissimilar to that of embodiment 1, and is asshown in FIGS. 9A, 9B.

<<Manufacturing Method>>

In this embodiment the process order is such that the step F is betweenthe step B and step C of the embodiment 1. For the order of processes,the process order of from FIG. 12 to FIG. 15 becomes the order ofA→B→F→C→D→E→G→H. The mask pattern is such that the scan signal line G1,scan electrode GT and contra-voltage signal line CL are separated whilea pattern of the transparent conductive layer g2 of each terminal and apattern of the contra-voltage signal line CL are formed in the samemask.

With such an arrangement, letting the counter electrode be transparentmakes it possible to improve the maximum transmissivity by about 16% (inthis embodiment 15.9%), which in turn permits the transmissivity of theliquid crystal display panel PNL to become 4.4%, or more or less.

Embodiment 3

This embodiment is the same as the embodiment 1 and embodiment 2 exceptfor the following points. A plan view diagram of pixels is shown in FIG.21. Hatched portions in the drawing indicate a transparent conductivefilm g2. <<Counter Electrode CT>>

In this embodiment the counter electrode CT is comprised of atransparent conductive film g2. This transparent conductive film g2 ismade of a sputtering-fabricated transparent conductive film(Indium-Tin-Oxide ITO: Nesa film) as in the embodiment 1, and is formedto a thickness of from 100 to 2,000 Á (in this embodiment, a filmthickness of about 1,400 Á).

<<Contra-Voltage Signal Line CL>>

The contra-voltage signal line CL is formed of a transparent conductivefilm g2, and is designed so that it is integral with the counterelectrode CT.

<<Manufacturing Method>>

In this embodiment the order of process steps is such that the step F isadded between the step B and step C of embodiment 1. For the order ofprocesses, the process order of from FIG. 12 to FIG. 15 becomes theorder of A→B→F→C→D→E→F→G→H. The mask pattern is such that a pattern ofthe scan signal line G1 and scan electrode GT and that of thecontra-voltage signal line CL are formed in independent masks.

With this embodiment, letting both the pixel electrode and the counterelectrode be transparent makes it possible to further improve themaximum transmissivity during white displaying by about 50% (in thisembodiment 47.7%) beyond the embodiment 1 or embodiment 2, resulting inthe liquid crystal display panel PNL being about 5.6% in transmissivity.

Embodiment 4

This embodiment is the same as the embodiment 1 and embodiment 3 exceptfor the following points. A plan view diagram of pixels is shown in FIG.22. Hatched portions in the drawing indicate a transparent conductivefilm g2. <<Contra-voltage Signal Line CL>>

The contra-voltage signal line CL is comprised of a conductivetransparent film g1. In this embodiment, Cr is used for the conductivefilm g1. Additionally, in order to connect between the contra-voltagesignal line CL and the counter electrode CT, anodization is not carriedout. In addition, a through-hole PH is formed in the gate insulationfilm GI. In addition, the conductive film g1 may be made from Ta, Ti,Mo, W, Al or an alloy thereof other than Cr, or alternatively it may beformed of a clad structure including a lamination of elements.

<<Manufacturing Method>>

In this embodiment the step B of the embodiment 1 is deleted. Inaddition, the through-hole PH is formed at the step E while forming boththe pixel electrode PX and the counter electrode CT simultaneously usingthe same mask.

In this embodiment, in addition to the effects of the embodiment 1 andembodiment 3, reducing the resistivity of the contra-voltage signal lineCL provides for a smooth transmission of a voltage between counterelectrodes; and reducing the voltage distortion makes it possible tosuppress crosstalk (lateral smear) occurring in the horizontaldirection.

In addition, forming the pixel electrode PX and counter electrode CTsimultaneously using the same mask permits the step F as performed twotimes in the embodiment 4 to be formulated into a single step, therebyimproving the productivity as well.

Embodiment 5

This embodiment is the same as the embodiment 1 and embodiment 4 exceptfor the following points. A plan view diagram of pixels is shown in FIG.23. Hatched portions in the drawing indicate a transparent conductivefilm g2.

<<Counter Electrode CT>>

In this embodiment, only the central counter electrode CT is made of atransparent conductive film g2. Those counter electrodes that neighborimage signal lines are each formed of a metal film in a way integralwith the contra-voltage signal lines.

In this embodiment, in addition to the effects of the embodiment 1 andembodiment 4, it becomes possible by making opaque the counterelectrodes neighboring the image signal lines to suppress crosstalkassociated with image signals. The reason for this is as indicated inthe section of the operation.

Embodiment 6

A respective one of the embodiments 2 and 3 is arranged such that boththe counter electrode signal line CL and the counter electrode CT areformed of the transparent conductive layer g2.

In this case, this embodiment is able to achieve significant reductionof the resistance value of the counter electrode signal line CL byemploying an arrangement shown in FIGS. 24A-C.

FIG. 24A is a plan view diagram showing part of the counter electrodesignal line CL of FIG. 20, while FIG. 24B is a sectional diagram takenalong line b-b of FIG. 24A.

In the drawing, a difference from FIG. 20 is that the counter electrodesignal line CL consists of a double-layer structure, wherein an Al layer10 that is less in resistance value is formed as its lower layer with anITO film 11 formed overlying this Al layer 10 so that it completelycovers the Al layer 10. And, the counter electrode CT is constitutedfrom an extension portion of said ITO film 11.

With such an arrangement, it is possible to achieve reduction of theresistivity of the counter electrode signal line CL while at the sametime preventing electrical short-circuiting between it and anotherconductive layer (e.g., image signal line DL) through an interlayerdielectric film due to the presence of a beard-like projection, called awhisker, which occurs in the Al layer 10.

More specifically, while it has been known that the Al layer 10 wouldexperience generation of a whisker during fabrication of the interlayerdielectric film overlying the layer with respect to the image signalline DL resulting in creation of the harmful effect stated above, it hasbeen affirmed that such whisker production will no longer take placewhen forming the ITO film to completely cover this Al layer 10.

Furthermore, in FIG. 24C the counter electrode CT is constituted from adouble or duplex lead—in this embodiment, a lead of an ITO film 11 isformed covering a lead of the Al layer 10. Because the vicinity of thecenter line of such lead is low in transmissivity even where a voltageis applied between electrodes, any aperture ratio reduction will hardlyoccur even where an opaque metal lead is disposed as in this example.

By employing the duplex lead for either the counter electrode or thepixel electrode, it is possible to greatly suppress open circuit defectsof electrodes which will become problematic in large-size screens.

Embodiment 7

<<Active-Matrix Liquid Crystal Display Device>>

An explanation will be given of an embodiment which applies the presentinvention to an active-matrix color liquid crystal display device. Notehere that in the drawings to be explained below, those elements havingthe same functions are designated by the same reference characters, andany repetitive explanation thereof will be omitted.

<<Planar Arrangement of Matrix Section (Pixel Section)>>

FIG. 25 is a plan view diagram showing one pixel along with the nearbyportions of the active-matrix color liquid crystal display device of thepresent invention. (Hatched portions in the drawing designate atransparent conductive film il).

As shown in FIG. 25, each pixel is disposed within a crossover orintersection region (within a region surrounded by four signal lines) ofa scan signal line (gate signal line or horizontal signal line) G1, acontra-voltage signal line (counter electrode lead) CL, and twoneighboring image signal lines (drain signal lines or vertical signallines) DL. Each pixel includes a thin-film transistor TFT, storagecapacitor Cstg, pixel electrode PX, and counter electrode CT. The scansignal line G1 and contra-voltage signal line CL extend laterally in thedrawing, and a plurality of similar lines are disposed in the up/downdirection. The image signal line DL extends in the up/down direction,and plural similar lines are disposed in the lateral direction. Thepixel electrode PX is formed of a transparent conductive film il and iselectrically connected to the thin-film transistor TFT via a sourceelectrode SD1; and the counter electrode CT also is formed of thetransparent conductive film il and is electrically connected to thecontra-voltage signal line CL.

The pixel electrode PX and the counter electrode CT are designed tooppose each other for control of the optical state of a liquid crystalLC by using an electric field between each pixel electrode PX andcounter electrode CT to thereby control the display. The pixel electrodePX and counter electrode are arranged to have a comb-like shape, each ofwhich becomes an elongate electrode in the up/down direction of thedrawing.

The line number 0 of counter electrodes CT within a single pixel isdesigned so that it has the relation of 0=P+I with no exceptions withrespect to the line number (number of comb teeth) of pixel electrodes PX(in this embodiment, 0=3, and P=2). This setup is in order toalternately dispose the counter electrodes CT and pixel electrodes PXand also force a counter electrode CT to neighbor an image signal lineDL with no exceptions. In this way, it becomes possible for the counterelectrode CT to shield electric flux lines from such image signal lineDL to ensure that an electric field between the counter electrode CT andpixel electrode PX receive no influence from an electric field createdfrom the image signal line DL. As counter electrodes CT are constantlysupplied with a voltage potential from the outside via contra-voltagesignal lines CL to be described later, the potential remains stabilized.Due to this, even when adjacent to the image signal line DL, anypotential variation hardly occurs. In addition, due to this, thegeometric position of the pixel electrode PX becomes far from the imagesignal line DL; therefore, any possible parasitic capacitance betweenthe pixel electrode PX and image signal line DL decreases significantly,thereby also enabling suppression of variation of a pixel electrodepotential Vs due to an image signal voltage(s). These characteristics inturn make it possible to suppress crosstalk (image quality defectscalled the longitudinal smear) occurring in the up/down direction.

Let each pixel electrode PX and counter electrode CT be 6 μm inelectrode width. This is in view of the fact that a sufficiently largervalue than the thickness, 3.9 μm, of a liquid crystal layer to be laterdescribed is set in order to apply a sufficient electric field to theentire liquid crystal layer with respect to the thickness direction ofthe liquid crystal layer while letting it be as fine as possible inorder to enlarge the aperture ratio. In addition, the electrode width ofimage signal lines DL is 8 μm, which is slightly wider than that ofpixel electrodes PX and counter electrodes CT in order to prevent anopen circuit. Here, the electrode width of image signal lines DL is setat a specified value that is less than or equal to twice the electrodewidth of the neighboring counter electrode CT. Alternatively, in caseswhere the electrode width of image signal lines DL was determined fromthe productivity of the yield, the electrode width of counter electrodesCT that neighbor image signal lines DL is set to be greater than orequal to half of the electrode width of image signal lines DL. This isin order to allow the counter electrodes CT on both sides to absorbelectric flux lines generated from image signal lines DL respectively.For good absorption of electric flux lines produced from a certainelectrode width, it is required to use an electrode that has itselectrode width equal to or wider than such certain electrode width.Accordingly, by taking into consideration that the counter electrodes CTon both sides may absorb those electric flux lines generated from half(4 μm for each) of the electrode of an image signal line DLrespectively, the electrode width of a counter electrode CT neighboringupon an image signal line DL is set to be greater than or equal to ½.This eliminates generation of crosstalk due to the influence of imagesignals—in particular, in the up/down direction (longitudinalcrosstalk).

Scan signal lines G1 are designed to have an electrode width set tosatisfy the resistance value that permits a scanning voltage to besufficiently applied to the gate electrode GT of a pixel on theterminate end side (on the opposite side of a scan electrode terminalGTM to be described later). Regarding contra-voltage signal lines CLalso, the electrode width is set to satisfy the resistance value thatpermits a contra-voltage to be sufficiently applied to the counterelectrode CT of a terminate-end pixel (a pixel farthest from common buslines CB1 and CB2 to be later described, i.e., a pixel lying midwaybetween CB1 and CB2).

On the other hand, the electrode distance between a pixel electrode PXand counter electrode CT is varied with the liquid crystal materialbeing used. This is in order to guarantee that, in view of the fact thatthe electric field intensity for achievement of the maximumtransmissivity is different for different liquid crystal materials, thesetup of the electrode distance as per a liquid crystal material letsthe maximum transmissivity be obtainable within the range of the maximalamplitude of a signal voltage set by the withstanding voltage of theimage signal drive circuit being used (signal-side driver). When using aliquid crystal display material to be described later, the electrodedistance becomes 16 μm.

<<Sectional Structure of Matrix Section (Pixel Section)>>

FIG. 26 is a sectional diagram at cut line 6-6 of FIG. 25; FIG. 27 is asectional diagram of a thin-film transistor TFT at line 7-7 of FIG. 25;and FIG. 28 is a sectional diagram of a storage capacitor Cstg at line8-8 of FIG. 25.

As shown in FIG. 26 to FIG. 28, a thin-film transistor TFT and storagecapacitor Cstg plus electrode group are formed on the side of the lowertransparent glass substrate SUB1 with a liquid crystal layer LC beingused as a reference, whereas a color filter FIL and optical shield blackmatrix pattern BM are formed on the side of the upper transparent glasssubstrate SUB2.

In addition, alignment films ORI, ORI2 for controlling the initialalignment of the liquid crystal are provided on the inside (liquidcrystal LC side) surfaces of the transparent glass substrates SUB1,SUB2, respectively, whereas polarizer plates (Cross Nicol layout) withpolarization axes laid out at right angles to each other are provided onthe outer surfaces of the transparent glass substrates SUB1, SUB2,respectively.

<<TFT Substrate>>

A detailed explanation will first be given of an arrangement on the sideof the lower transparent glass substrate SUB1 (TFT substrate).

<<Thin-Film Transistor TFT>>

A thin-film transistor TFT operates in a way such that upon applicationof a positive bias to its gate electrode GT, the channel resistancebetween the source and drain decreases; and, in the absence of anybiasing thereto, the channel resistance increases.

As shown in FIG. 27, the thin-film transistor TFT has a gate electrodeGT, gate insulation film GI, i-type semiconductor layer AS made ofi-type (intrinsic: without doping any impurity for determining theconductivity type) amorphous silicon (Si), and a pair of a sourceelectrode SD1 and drain electrode SD2. Additionally, in view of the factthat the source and drain are inherently determinable by a bias polaritytherebetween and that in circuitry of this liquid crystal display deviceits polarity will be inverted during operations, it should be understoodthat the source and drain are interchangeable during operations.However, in the explanation given below, one of them will be fixedlyreferred to as the “source”, whereas the other is referred to as the“drain” for purposes of convenience only.

<<Gate Electrode GT>>

The gate electrode GT is formed to be continuous with a scan signal lineG1, wherein a partial region of the scan signal line G1 is arranged tobecome the gate electrode GT. The gate electrode GT is the part that isbeyond the active regions of the thin-film transistor TFT. In thisembodiment the gate electrode GT is formed of a single-layer conductivefilm g3. The conductive film g3 may be a sputter-fabricatedchromium-molybdenum alloy (Cr—Mo) film, although the invention is notexclusively limited thereto.

<<Scan Signal Line G1>>

The scan signal line G1 is formed of a conductive film g3. Thisconductive film g3 of the scan signal line G1 is fabricated at the sameprocess step with the formation of the conductive film g3 of the gateelectrode GT so that these elements are formed integrally with eachother. This scan signal line G1 permits supply of a gate voltage Vg fromexternal circuitry to the gate electrode GT. In this example theconductive film g3 may be a sputter-fabricated chromium-molybdenum alloy(Cr—Mo) film. Note that the scan signal line G1 and gate electrode GTshould not be limited only to the chromium-molybdenum alloy; forexample, these may be designed to have a double-layered structure ofaluminum or aluminum alloy wrapped by chromium-molybdenum forresistivity reduction. Furthermore, its crossover portion with an imagesignal line DL may be made fine in order to reduce the possibility ofshort-circuiting with the image signal line DL; or, alternatively, acrotch or Y-bent configuration may be employed in order to enablecutaway separation by laser trimming even upon occurrence ofshort-circuiting.

<<Contra-Voltage Signal Line CL>>

The contra-voltage signal line CL is formed of a conductive film g3.This contra-voltage signal line CL's conductive film g3 is formed at thesame process step with the conductive film g3 of gate electrode GT andscan signal is line G1 plus counter electrode CT, and is arranged to beable to offer electrical connectivity to the counter electrode CT. Thiscontra-voltage signal line CL is for supplying a contra-voltage Vcomfrom external circuitry to the counter electrode CT.

In addition, the contra-voltage signal line CL should not be limited tochromium-molybdenum alloys only; for example, it may be designed to havea double-layered structure of aluminum or aluminum alloy wrapped bychromium-molybdenum for resistivity reduction.

Furthermore, its crossover portion with an image signal line DL may bemade thinner in order to reduce the possibility of short-circuiting withthe image signal line DL; or, alternatively, a crotch or Y-bentconfiguration may be employed in order to enable cutaway separation bylaser trimming even upon occurrence of short-circuiting.

<<Dielectric Film GI>>

The dielectric film GI is for use as a gate insulation film for givingan electric field to the semiconductor layer AS along with the gateelectrode GT at the thin-film transistor TFT. The dielectric film GI isformed to overlie the gate electrode GT and scan signal line G1. As thedielectric film GI, a silicon nitride film is chosen which was formed byplasma CVD for example to a thickness ranging from 2,500 to 4,500 Á (inthis embodiment, about 3,500 Á). The dielectric film G1 also functionsas an interlayer dielectric film between the scan signal line G1 andcontra-voltage signal line CL on one hand and the image signal line DLon the other hand to thereby contribute to electrical isolation of them.In addition, the dielectric film GI is patterned for all-at-a-timefabrication by using the same photomask as that for a protective filmPSV1 to be later described.

<<i-Type Semiconductor Layer AS>>

The i-type semiconductor layer AS is made of amorphous silicon and isformed to a thickness of from 200 to 2,500 Á (about 1,200 Á in thisembodiment).

A layer d0 is an N(+) type amorphous silicon semiconductor layer withphosphorus (P) doped therein for ohmic contact, which is left only at aportion where the i-type semiconductor layer AS is present on the lowerside, while a conductive layer d3 exists on the upper side thereof.

The i-type semiconductor layer AS and layer d0 are also provided betweenboth intersections (crossover sections) of the scan signal line G1 andcontra-voltage signal line CL with respect to the image signal line DL.The i-type semiconductor layer AS at these intersections suppressesshort-circuiting between the scan signal line G1 and contra-voltagesignal line CL and the image signal line DL at such cross points.

<<Source Electrode SD1, Drain Electrode SD2>>

Each of the source electrode SD1 and drain electrode SD2 is constitutedfrom a conductive film d3 in contact with the N(+) type semiconductorlayer d0.

The conductive film d3 may be a chromium-molybdenum alloy (Cr—Mo) filmthat is formed by sputtering to a thickness of from 500 to 3,000 Á(about 2,500 Á in this embodiment). As the Cr—Mo film is inherently lowin stress, a film thickness can be formed comparatively thickly, whichin turn contributes to achievement of low resistivity of the leads. TheCr—Mo film is also excellent in adhesiveness with the N(+) typesemiconductor layer d0. The conductive film d3 may be formed of ahigh-melting-point metal (Mo, Ti, Ta, W) film or high-melting-pointmetal silicide (MOSi₂, TiSi₂, TaSi₂. WSi₂) film in place of the Cr—Mofilm; or, alternatively, it may be designed to have a multilayerstructure with aluminum or the like.

After having patterned the conductive film d3 using a mask pattern, theconductive film d3 is used as a mask to remove the N(+) typesemiconductor layer d0. In other words, specified portions of the N(+)type semiconductor layer d0 residing on the i-type semiconductor layerAS which exclude those at the conductive film d1 and conductive film d2are removed in a self-align fashion. At this time, since the N(+) typesemiconductor layer d0 is etched so that all portions corresponding toits thickness are removed, the i-type semiconductor layer AS will alsobe slightly etched away at its surface portion; the extent of suchetching may be controlled by adjustment of the etching time.

<<Image Signal Line DL>>

The image signal line DL is comprised of a conductive film d3 that is atthe same layer of the source electrode SD1 and drain electrode SD2. Inaddition, the image signal line DL is formed integrally with the drainelectrode SD2. In this example the conductive film d3 may be achromium-molybdenum alloy (Cr—Mo) film that is formed by sputtering to athickness of from 500 to 3,000 Á (about 2,500 Á in this embodiment). Asthe Cr—Mo film is low in stress, a film can be formed comparativelythickly, which in turn contributes to achievement of low resistivity ofthe leads. The Cr—Mo film is also excellent in adhesiveness with theN(+) type semiconductor layer d0. The conductive film d3 may be formedof a high-melting-point metal (Mo, Ti, Ta, W) film or high-melting-pointmetal silicide (MOSi₂, TiSi₂, TaSi₂, WSi₂) film in the alternative ofthe Cr—No film, or, alternatively, it may be designed to have amultilayer structure with aluminum or the like.

<<Storage Capacitor Cstg>>

The conductive film d3 is formed to overlap the contra-voltage signalline CL at a source electrode SD2 portion of a thin-film transistor TFT.As apparent from FIG. 28 also, this overlapping constitutes a storagecapacitor (electrolytic capacitive element) Cstg with the sourceelectrode SD2 (d3) as its one electrode and with the contra-voltagesignal CL as its remaining electrode. The dielectric film of the storagecapacitor is formed of the film GI that is used as the gate insulationfilm of the thin-film transistor TFT.

As shown in FIG. 25, when looking planarly, the storage capacitor Cstgis formed at part of the contra-voltage signal line CL.

<<Protective Film PSV1>>

A protective film PSV1 is provided to overlie the thin-film transistorTFT. The protective film PSV1 is formed to mainly protect the thin-filmtransistor TFT from humidity or the like, and so one that is high intransparency and good in moisture vapor resistance is used. Theprotective film PSV1 is made of a silicon oxide film or silicon nitridefilm as fabricated by a plasma CVD apparatus, for example, to a filmthickness ranging from 0.3 to 1 μm or therearound.

The protective film PSV1 has been removed to expose the externalconnection terminals DTM, GTM. With regard to a relation of thethicknesses of the protective film PSV1 and the gate insulation film GI,the former is made is thick in light of the protection effect, whereasthe latter is rendered thinner in view of the mutual conductance of thetransistor. In addition, the protective film PSV1 is patterned forsimultaneous fabrication by use of the same photomask as that for thedielectric film GI. In addition, through-holes TH2 and TH1 are providedat a pixel section, for electrical connection between the contra-voltagesignal line CL and a counter electrode CT to be later discussed and alsofor electrical connection between the source electrode SD2 and pixelelectrode PX. At the through-hole TH2, a hole is defined extending tothe g3 layer due to simultaneous fabrication of the protective film PSV1and dielectric film GI; and, at the through-hole TH1, a hole is definedreaching the d3 layer due to blocking by d3.

<<Pixel Electrode PX>>

The pixel electrode PX is formed of a transparent conductive layer il.This transparent conductive film il is made of a transparent conductivefilm (Indium-Tin-Oxide ITO: Nesa film) formed by sputtering to athickness of 100 to 2,000 Á (in this embodiment, about 1,400 Á). Inaddition, the pixel electrode PX is connected via the through-hole TH1to the source electrode SD2.

Making the pixel electrode transparent as in this embodiment leads toimprovement of the maximum optical transmissivity when performing whitedisplaying due to rays of light passing through such portion; thus, itbecomes possible to generate a brighter display than in the case ofusing opaque pixel electrodes. At this time, as will be described later,the polarizer plate layout is arranged (in the normally-black mode) sothat liquid crystal molecules retain their initial alignment state inthe absence of a voltage applied thereto to achieve black displayingunder such condition; consequently, even though the pixel electrodes aremade transparent, no light rays penetrate such portions to therebyenable displaying of black with good quality. This in turn makes itpossible to improve the maximum transmissivity while achieving asufficient contrast ratio.

<<Counter Electrode CT>>

The counter electrode CT is formed of a transparent conductive layer il.This transparent conductive film il is made of a transparent conductivefilm (Indium-Tin-Oxide ITO: Nesa film) formed by sputtering to athickness of 100 to 2,000 Á (in this embodiment, about 1,400 Á). Inaddition, the counter electrode CT is connected via the through-hole TH2to the contra-voltage signal line CL.

The counter electrode CT is arranged so that a contra-voltage Vcom isapplied thereto. In this embodiment the contra-voltage Vcom is set at aselected potential level which is lower by a specified degree than anintermediate DC voltage potential that is midway between the minimumlevel of drive voltage Vdmin and maximum level of drive voltage Vdmax asapplied to the image signal line DL, which specified degree correspondsto a feed-through voltage ΔVs generated when turning off the thin-filmtransistor TFT, although an AC voltage may alternatively be appliedthereto in cases where it is required that the power supply voltage ofan integrated circuit for use in image signal drive circuitry be reducedin potential down at one half thereof.

<<Color Filter Substrate>>

Next, turning back to FIG. 25 and FIG. 26, a detailed explanation willbe given of an arrangement of the side of the upper transparent glasssubstrate SUB2 (color filter substrate).

<<Optical Shield Film BM>>

An optical shield film BM (so-called black matrix) is formed on the sideof the upper transparent glass substrate SUB2 for preventing reductionof the contrast ratio or the like which otherwise occurs due to outwardemission of transmission light from unnecessary gaps (gaps other thanthat between the pixel electrode PX and counter electrode CT) toward thedisplay plane side.

The optical shield film BM also functions to prevent either externallight or backlight rays from falling onto the i-type semiconductor layerAS. More specifically, the i-type semiconductor layer AS of thethin-film transistor TFT is sandwiched by the optical shield film BM andthe gate electrode GT of relatively large size which are at the upperand lower locations to thereby eliminate hitting of externally incomingnatural light and backlight rays.

The optical shield film BM shown in FIG. 25 is arranged so that itlinearly extends along the lateral direction over the thin-filmtransistor TFT. This pattern is one example; however, alternatively, itmay be designed into a matrix form with openings defined like holes. Atcertain portions at which the electric field direction is disturbed suchas comb-shaped electrode ends, the display at such portions; is inone-to-one correspondence to image information within pixels so thatblack is obtained in the case of black and white for white; accordingly,such can be utilized as part of the display. In addition, a gap betweenthe counter electrode CT and image signal line DL in the up/downdirection of the drawing is optically shielded by a light shield layerSH that was formed at the same process step of the gate electrode GT.Whereby, the up/down-directional light shielding in the right/left orlateral direction can be optically shielded with a high accuracyequivalent to the alignment accuracy of TFT processes, which in turnmakes it possible to establish a boundary of the light shield layer SHbetween electrodes of counter electrodes CT that neighbor image signallines DL thereby enabling further enlargement of the opening as comparedto the case of optical shielding due to an optical shield film BM thatdepends on the positional alignment accuracy of the upper and lowersubstrates.

The optical shield film BM has a shielding effect with respect to lightand is formed of a highly insulative film for elimination of any badinfluence on an electric field between the pixel electrode PX andcounter electrode CT; and, in this embodiment, it is made of a resistmaterial mixed with black pigment formed to a thickness of about 1.2 μm.

The optical shield film BM is linearly formed in the lateral directionwith respect to those pixels in each row so that effective displayregions at each row are partitioned by this line. Thus, the contour lineof each row pixel is made clear by the optical shield film BM. In otherwords, the optical shield film BM functions as the black matrix whilealso functioning to optically shield the i-type semiconductor layer AS.

The optical shield film BM is also formed at the periphery to have awindow frame-like shape, whose pattern is formed in a way continuouswith the pattern of the matrix section shown in FIG. 25. The opticalshield film BM at the periphery is extended to the outside of a sealsection SL thereby preventing leakage light, such as reflection lightdue to practical mount equipment, such as personal computers, fromentering the matrix section, while at the same time preventing the lightsuch as backlight from leaking toward the outside of the display area.On the other hand, this optical shield film BM is limited in location sothat it resides within an inside area that is smaller by about 0.3 to1.0 mm than the edge of the substrate SUB2, and also is formed excludingcutaway regions of the substrate SUB2.

<<Color Filter FIL>>

Same as the embodiment 1.

<<Overcoat Film OC>>

Same as Embodiment 1.

<<Liquid Crystal layer, Alignment Film & Polarizer Plate>>

Same as Embodiment 1.

<<Configuration of Matrix Vicinity>>

Same as Embodiment 1.

<<Gate Terminal Section>>

FIG. 29A is a plan view showing a connection structure from the displaymatrix's scan signal line G1 up to its external connection terminal GTM,while FIG. 29B shows a cross-section at line B-B of FIG. 29A. Note thatthe drawing corresponds to the FIG. 5 right center vicinity, wherein ahatched part is represented by one straight line shape for purposes ofconvenience.

In the drawing the Cr—Mo layer g3 is hatched for clarity purposes only.

The gate terminal GTM is comprised of the Cr—Mo layer g3 and atransparent conductive layer il that is used for protecting the surfaceand for improving the reliability of connection with a TCP (Tape carrierPackage). This transparent conductive film il employs a transparentconductive film ITO that was formed at the same process step with theforming of the pixel electrode PX.

In the plan view diagram, the dielectric film G1 and protective filmPSV1 are formed on the right side of its boundary, wherein the terminalsection DTM placed at the left end is arranged to be exposed from themfor enabling electrical contact with external circuitry. Although in thedrawing only one pair of the gate line G1 and gate terminal is depicted,in the actual implementation, a plurality of such line pairs are laidout in the up/down direction as shown in FIG. 29A to constitute theterminal group Tg (FIG. 5), is wherein the left end of the gate terminalis extended beyond the cutting region of the substrate to beshort-circuited by a lead SHg (not shown) during the manufacturingprocesses. This is useful for elimination of electrostatic breakdownduring rubbing of the alignment film ORI1 or the like.

<<Drain Terminal DTM>>

FIG. 30A is a plan view diagram showing connection from the image signalline DL to its external connection terminal DTM; and FIG. 30B showsacross-section at line B-B of FIG. 30A. Note that the drawingcorresponds to the FIG. 5 upper right vicinity, and that, although thedirection of the drawing is changed for convenience purposes, the rightend direction corresponds to the upper end of the substrate SUB1.

“TSTd” denotes a test terminal to which external circuitry is notconnected and which is widened to have a width greater than that of thelead section to thereby permit contacting by a probe needle or the like.Similarly, the drain terminal DTM also is widened to be wider in widththan the lead portion to enable connection with external circuitry.External connection drain terminals DTM are laid out in the up/downdirection; and, as shown in FIG. 5, the drain terminals DTM constitutethe terminal group Td (suffix eliminated) and are designed to furtherextend beyond the cut line of the substrate SUB1, all of which areshort-circuited by a lead SHd (not shown) during the manufacturingprocesses for prevention of electrostatic breakdown. As shown in FIG. 8,test terminals TSTD are formed at alternate ones of the image signallines DL.

The drain connection terminal DTM is formed of a transparent conductivelayer il, and is connected to an image signal line DL at a certain partfrom which the protective film PSV1 is removed. This transparentconductive film il makes use of a transparent conductive film ITO thatwas formed at the same process step of forming pixel electrodes PX as inthe case of the gate terminal GTM.

An extension lead from the matrix section up to the drain terminalsection DTM is such that a layer d3 is arranged at the same level as theimage signal line DL.

<<Counter Electrode Terminal CTM>>

FIG. 31A is a plan view diagram showing connection from thecontra-voltage signal CL up to its external connection terminal CTM; andFIG. 31B shows a cross-section at line B-B of FIG. 31A. Note that thedrawing corresponds to the upper left part of FIG. 5 or therearound.

Respective contra-voltage signal lines CL are bundled by a common busline CB to be drawn out toward the counter electrode terminal CTM. Thecommon bus line CB is structured from a lamination of a conductive layer3 on the conductive layer g3 with the transparent conductive film ilelectrically connected between them. This is in order to reduce theresistivity of the common bus line CB to ensure that a contra-voltage issufficiently supplied from external circuitry to each contra-voltagesignal line CL. In the structure shown herein, a feature thereof lies inthe ability to reduce the resistance of the common bus line withoutnewly loading any extra conductive layers.

The counter electrode terminal CTM is structured from the conductivelayer g3 and the transparent conductive layer il as laminated thereon.This transparent conductive film il employs a transparent conductivefilm ITO that was formed at the same process step of forming pixelelectrodes PX, as in other terminals. The conductive layer g3 is coveredwith the transparent conductive layer il, which is excellent indurability, in order to let the transparent conductive layer il protectits surface for elimination of electrolytic corrosion. In addition,connection of the transparent conductive layer il with the conductivelayer g3 and conductive layer d3 is effected by conduction via athrough-hole(s) as formed in the protective film PSV1 and dielectricfilm GI.

On the other hand, FIG. 32A is a plan view showing connection fromanother end of the contra-voltage signal CL up to its externalconnection terminal CTM2; and FIG. 32B is a sectional view taken alongline B-B of FIG. 32A. Note that the drawing corresponds to the upperright part of FIG. 5 or therearound. Here, at the common bus line CB2,the remaining ends (on the gate terminal GTM side) of respectivecontra-voltage signal lines CL are bundled to be drawn out toward thecounter electrode terminal CTM2. A difference from the common bus lineCB1 lies in forming the conductive layer d3 and transparent conductivelayer il for electrical insulation is provided with the scan signal lineG1. In addition, electrical insulation with the scan signal line G1.

<<Display Device Overall Equivalent Circuit>>

An equivalent circuit of the display matrix section and its peripheralcircuit connection diagram are shown in FIG. 33. Although this drawingis a circuit diagram, it has been illustrated in a way corresponding tothe actual geometric layout. “AR” is a matrix array with a plurality ofpixels laid out two-dimensionally.

In the drawing, “X” denotes image signal lines DL to which with suffices“G”, “B” and “R” are appended, which stand for green, blue and redpixels, respectively. “Y” denotes scanning signal lines G1 with suffices1, 2, 3, . . . , “end” are appended to denote the order of sequence ofthe scan timing.

The scan signal lines Y (suffix eliminated) are connected to a verticalscanning circuit V, while the image signal lines X (suffix omitted) arecoupled to an image signal driving circuit H.

“SUP” denotes circuitry that includes a power supply circuit forobtaining a plurality of stabilized voltage sources voltage-divided froma single voltage source along with a circuit or circuits for conversionof information for a CRT (cathode-ray tube) from a host (upper-level or“supervisory” arithmetic processing device) into information for usewith a TFT liquid crystal display device.

<<Driving Method>>

Several drive waveforms of the liquid crystal display device of thisembodiment are shown in FIG. 34. Assume that a contra-voltage Vc is keptconstant in potential. A scan signal Vg takes the ON level once per scanperiod, and during the remaining periods, it is at the OFF level. Animage signal voltage is applied in a way such that the positive polarityand negative polarity are inverted once per frame for transmission to asingle pixel at an amplitude equal to twice the voltage required to beapplied to the liquid crystal layer. Here, the image signal voltage Vdis inverted in polarity on a one-per-column basis; and, such polarityinversion is also done on a one-per-row basis. This results inachievement of an arrangement that lets polarity-inverted pixelsneighbor each other in the up/down and right/left directions, therebymaking it possible to inhibit flicker and crosstalk (smear). Inaddition, the contra-voltage Vc is set at a selected potential that ispotentially lower by a predefined degree from the center voltage ofpolarity inversion of the image signal voltage. This is in order tocompensate for a feed-through voltage occurring when the thin-filmtransistor element is switched from ON to OFF, and is performed in orderto apply to the liquid crystal an AC voltage with a smaller DCcomponent. This is because upon application of DC, the liquid crystalmight suffer from severe after imaging and degradation or the like.

In addition thereto, use of an AC voltage as the contra-voltage makes itpossible to lower the maximum amplitude of an image signal voltage,which in turn makes employment of image signal drive circuits(signal-side drivers) that are low in withstanding voltage possible.

<<How Storage Capacitor Cstg Works>>

Same as Embodiment 1.

<<Manufacturing Method>>

An explanation will next be given of a method of manufacturing thesubstrate SUB1 assembly of the above-mentioned liquid crystal displaydevice with reference to FIG. 35 to FIG. 37. Note that in thesedrawings, the characters centrally indicated therein are process namesabbreviated, wherein a flow of fabrication process steps is shown whileindicating on its left side a cross-section of the thin-film transistorTFT part shown in FIG. 27 along with a cross-section at or near the gateterminal shown in FIG. 29 on the right side. Except for a process step Band step D, step A-step I are partitioned in a way corresponding to eachphotographic processing, wherein any one of such process steps indicatesthe stage where the fabrication processing after the photographicprocess has been completed with a photoresist removed already. Note herethat the term “photographic processing” as used herein refers to aseries of operations from deposition of a photoresist through selectiveexposure using a mask up to development thereof, and any repetitiveexplanation will be omitted. An explanation will be given in accordancewith the process steps thus partitioned.

Step A, FIG. 35

A conductive film g3 made of Cr—Mo or the like is provided by sputteringon the lower transparent glass substrate SUB1 comprised of AN635 glass(Trade Name), to a thickness of 2,000 A. After photographic processing,the conductive film g3 is selectively etched by use of ammonium cerium(IV) nitrate. Thus, gate electrodes GT, scan signal lines G1,contra-voltage signal lines CL, gate terminals GTM, first conductivelayer of common bus lines CB1, first conductive layer of counterelectrode terminals CTM1, and more than one bus line SHg (not shown) forconnection of the gate terminals GTM are formed.

Step B, FIG. 35

After having introduced into a plasma CVD apparatus an ammonia gas andshiran gas plus nitrogen gas to provide a Si nitride film of 3,500 Áthick and then having introduced into the plasma CVD apparatus a shirangas and hydrogen gas to provide an i-type amorphous Si film of 1,200 Áthick, a hydrogen gas and phosphine gas are introduced into the plasmaCVD apparatus to thereby provide an N(+) type amorphous Si film to athickness of 300 Á.

Step C, FIG. 35

After photographic processing, the N(+) amorphous Si film and i-typeamorphous Si film are selectively etched by using SF₆ and CCl₄ as dryetching gases to thereby form more than one island of an i-typesemiconductor layer AS.

Step D, FIG. 36

A conductive film d3 made of Cr is provided by sputtering to a thicknessof 3000 Á. After photographic processing, the same liquid as that usedat the step A is used to etch the conductive film d3 to thereby formimage signal lines DL, source electrodes SD1, drain electrodes SD2, afirst conductive layer of common bus lines CB2, and more than one busline SHd (not shown) for short-circuiting the drain terminals DTM. Next,CCl₄ and SF₆ are introduced into the dry etching apparatus to etch theN(+) type amorphous Si film for selective removal of an N(+) typesemiconductor layer d0 between the source and drain.

Step E, FIG. 36

An ammonia gas and shiran gas plus nitrogen gas are introduced into theplasma CVD apparatus to provide a Si nitride film 0.4 μm thick. Afterphotographic processing, a protective film PSV1 and dielectric film GIare patterned by selectively etching the Si nitride film using SF₆ as adry etching gas.

Step F, FIG. 37

A transparent conductive film il made of an ITO film is provided bysputtering to a thickness of 1,400 Á. After photographic processing, thetransparent conductive film il is selectively etched using as an etchingliquid a mixed acid liquid of hydrochloric acid and nitric acid, therebyforming the uppermost layer of gate terminals GTM along with the secondconductive layer of drain terminals DTM and counter electrode terminalsCTM1 and CTM2.

<<Display Panel PNL & Driver Circuit Board PCB1>>

Same as Embodiment 1.

<<TCP's Connection Structure>>

Same as Embodiment 1.

<<Driver Circuit Board PCB2>>

Same as Embodiment 1.

<<Overall Arrangement of Liquid Crystal Display Module>>

Same as Embodiment 1.

As apparent from the foregoing, in this embodiment, making thecomb-shaped electrodes transparent in the same way as in the embodiment3 makes it possible to achieve the maximum optical transmissivity toeffect an improvement by about 50% during generation of a white display,while letting the liquid crystal display panel PNL become about 5.7% intransmissivity.

In addition, it becomes possible to simultaneously fabricate the ITOfilm for improvement of the reliability of elements, which in turn makesit possible to achieve both an improved reliability and productivity atthe same time.

A further advantage of this embodiment is that unlike the embodiments1-6 above, the embodiment is designed to employ the process of formingan ITO film overlying the protective film PSV1 which in turn makes itpossible to bring the counter electrode at the uppermost layer whileretaining good shield efficiency of leakage electric fields from imagesignal lines with crosstalk reduced.

A still further advantage is that the absence of any protective filmPSV1 in the pathway of electric flux lines for driving liquid crystalsbetween electrodes leads to elimination of any possible voltagereduction at such protective film PSV1 which in turn has enabled themaximal drive voltage value for liquid crystal drive to decrease inpotential from 7.5 Volt as in the embodiment 1 down to 5.0 Volt as inthis example.

With the scheme for driving liquid crystals by applying an electricfield extending substantially in parallel to the substrate surface, theprotective film must appear twice in the pathway of electric flux linesbetween electrodes so that the process required can be simplified whileimproving productivity.

Embodiment 8

This embodiment is the same as the embodiment 7 except for the followingpoints. A plan view of pixels is shown in FIG. 38. Hatched portions inthe drawing designate a transparent conductive film il.

<<Pixel Electrode PX>>

In this embodiment the pixel electrode PX is constituted from aconductive film d3 that is in the same layer as the source electrode SD1and drain electrode SD2. In addition, the pixel electrode PX is formedintegrally with the source electrode SD1.

With this embodiment, in addition to the effects of embodiment 1, it ispossible to avoid contact defects between the pixel electrode PX andsource electrode SD1 although this comes at a sacrifice of the opticaltransmissivity. Another advantage is that since one of the electrodes iscovered with the dielectric film (protective film PSV1), the possibilitythat a DC current flows in liquid crystals in the presence of alignmentfilm defects decreases resulting in elimination of liquid crystaldeterioration or the like, thus improving the reliability.

Embodiment 9

This embodiment is the same as the embodiment 7 except for the followingpoints. A plan view of pixels is shown in FIG. 39. Hatched portions inthe drawing indicate a transparent conductive film il.

<<Counter Electrode CT>>

In this embodiment the counter electrode CT is comprised of a conductivefilm g3 that is integral with the contra-voltage signal line CL.

With this embodiment, in addition to the effects of the embodiment 1, itis possible to avoid contact failures between the counter electrode CTand contra-voltage signal line CL although this does come at a sacrificeof the transmissivity. Another advantage is that since one of theelectrodes is covered with the dielectric film (protective film PSV1),the possibility that a DC current flows in liquid crystals in thepresence of alignment film defects decreases resulting in elimination ofliquid crystal deterioration, thereby improving the reliability.

Embodiment 10

This embodiment is the same as the embodiment 7 except for the followingpoints. A plan view of pixels is shown in FIG. 40. Hatched portions inthe drawing indicate a transparent conductive film il.

<<Optical Shield Film BM>>

An optical shield film BM (so-called black matrix) is formed on the sideof the upper transparent glass substrate SUB2 for preventing reductionof the contrast ratio or the like which otherwise occurs due to outwardemission of transmission light from unnecessary gaps (gaps other thanthat between the pixel electrode PX and counter electrode CT) toward thedisplay plane side. The optical shield film BM also functions to preventrays of either external light or backlight from falling onto the i-typesemiconductor layer AS. More specifically, the i-type semiconductorlayer AS of the thin-film transistor TFT is sandwiched by the opticalshield film BM and the gate electrode GT of larger size which are at theupper and lower locations to thereby eliminate hitting of externallyincoming natural light and backlight rays.

The optical shield film BM shown in FIG. 40 is arranged to extend in theup/down-and-right/left directions over the thin-film transistor TFTwhile having a matrix-like shape with holes defined at openings. Atcertain portions at which the electric field direction is disturbed suchas comb-shaped electrode ends, display at such portions is in one-to-onecorrespondence to image information within pixels so that black isobtained in the case of black and white is obtained for white;accordingly, such can be utilized as part of the display.

Another advantage of this embodiment is that unlike the embodiment 7,the optical shield film BM has a shielding ability against light rays,and is formed of a high-conductivity film to ensure that any electricfield of/from image signal lines DL hardly affects the electric fieldbetween the pixel electrode PX and counter electrode CT—in thisembodiment, it was comprised of a three-layered lamination structureconsisting of chromium oxide (CrO_(x)) and chromium nitride (CrN), pluschromium (Cr), which structure is formed from the surface of the opposedsubstrate SUB1 to a thickness of about 0.2 μm. At this time the chromiumoxide (Cro_(x)) is used to suppress reflection on the display plane.Additionally, the chromium (Cr) is provided at the uppermost layer ofoptical shield layer BM to permit external supply of a voltage to theoptical shield film BM.

The optical shield film BM is linearly formed in the right/leftdirection with respect to those pixels in each row so that effectivedisplay regions at each row are partitioned by this line. Thus, thecontour of each row pixel is made clear by the optical shield film BM.In other words, the optical shield film BM functions as a black matrixwhile simultaneously functioning to optically shield the i-typesemiconductor layer AS.

The optical shield film BM is also formed at the periphery into a windowframe-like shape, whose pattern is formed in a way continuous with thepattern of the matrix section shown in FIG. 25. The optical shield filmBM at the periphery is extended to outside of a seal section SL therebypreventing leakage light, such as reflection light due to practicalmount equipment, such as personal computers, from entering the matrixsection, while at the same time preventing the light such as backlightfrom leaking toward the outside of the display area. On the other hand,this optical shield film BM is limited in location so that it resideswithin an inside area smaller by about 0.3 to 1.0 mm than the edge ofthe substrate SUB2, and also is formed excluding cutaway regions of thesubstrate SUB2.

<<Overcoat Film OC>>

Same as Embodiment 1. Note however that one or more through-holes may beformed to enable a voltage potential to be given to the optical shieldfilm BM. It is preferable that as the voltage potential, connection beeffected to the contra-voltage Vc.

An advantage of this embodiment is that in addition to the effects ofthe embodiment 7, letting the optical shield film BM shield anyinfluence of electric fields from image signal lines DL prevents anelectric field, from being affected between the pixel electrode PX andcounter electrode CT. This eliminates crosstalk with image signal linesDL, which in turn enables avoidance of comet-tail-like blurred on-screenimage quality defects (smear). Additionally, it is also possible todownsize the region for optical shielding by the light shield layer SHand the transparent counter electrodes CT as disposed on the oppositesides of an image signal line DL, which in turn enables achievement ofhigher transmissivity.

Embodiment 11

FIGS. 43A to 43D are diagrams showing principles relating to apertureratio improvement of an active-matrix color liquid crystal displaydevice in accordance with this embodiment, wherein FIG. 43A is acharacteristic diagram showing a potential distribution inside of aliquid crystal layer upon application of a voltage to the electrodes,FIG. 43B is a diagram showing a realignment state of liquid crystalmolecules near or around the center of the liquid crystal layer, FIG.43C is a characteristic diagram showing a rotation angle α of liquidcrystal molecules shown in FIG. 43B, and FIG. 43D is one example of acharacteristic diagram showing a distribution of transmissivity of lightpassing through the upper/lower polarizer plates and upper/lowersubstrates plus a liquid crystal layer on electrodes and betweenelectrodes.

Here, the same as the embodiment 7 are provided except for the pointswhich follow.

In this embodiment, approximately 2×10⁻¹² N (Newton) was used as thetwist elastic modulus K2 of the liquid crystal layer.

When such a relatively large value of for example 10×10⁻¹² N (Newton) isused as the twist elastic modulus K2, almost all of the liquid crystalmolecules at the center over electrodes are kept at zero in rotationangle α as shown in FIG. 41B, resulting in the transmissivity at thecenter over. such electrodes approximating a value of a dark display.

On the other hand, it has been found that in this embodiment the liquidcrystal molecules at the center over electrodes also attempt to rotatecausing more than 50% of the average transmissivity of thetransmissivity of a portion “A” between electrodes to become theaverage-value transmissivity of the transmissivity at a portion “B” overelectrodes.

Consequently, the average transmissivity as a whole becomes theaverage-value transmissivity of the transmissivities at the portionsA+B, which is significantly increased.

As has been described above, the present invention is applicable todevices which employ liquid crystals and offers practical utility in theliquid crystal device manufacturing industry.

1. A liquid crystal display device comprising: first and secondsubstrates; a liquid crystal layer disposed between the first and secondsubstrates; a plurality of pixel regions formed by a plurality of gatesignal lines and a plurality of image signal lines formed over the firstsubstrate; a first insulating layer formed over the plurality of gatesignal lines; a plurality of thin film transistors connected to theplurality of gate signal lines; a second insulating layer formed overthe plurality of thin film transistors; a plurality of pixel electrodesconnected to the plurality of thin film transistors; a counter electrodeformed over the second insulating layer which is formed by a firsttransparent conductive layer; and a second transparent conductive layerand an external connection terminal disposed outside of the pluralitypixel regions; wherein the second transparent conductive layer is formedover the second insulating layer and is electrically connected to thecounter electrode and the external connection terminal; and wherein apart of each of the plurality of gate signal lines is disposed outsideof the plurality pixel regions and is covered by the second transparentconductive layer.
 2. A liquid crystal display device according to claim1, wherein the liquid crystal layer is driven by an electric field whichis generated between one of the plurality of pixel electrodes and thecounter electrode.
 3. A liquid crystal display device according to claim2, wherein a part of the second insulating layer is disposed between thepart of each of the plurality of gate signal line disposed outside ofthe plurality pixel regions and the second transparent conductive layer.4. A liquid crystal display device according to claim 2, wherein theliquid crystal display device is an in-plane switching type liquidcrystal display device.
 5. A liquid crystal display device according toclaim 4, wherein a part of the second insulating layer is disposedbetween the part of each of the plurality of gate signal line disposedoutside of the plurality pixel regions and the second transparentconductive layer.
 6. A liquid crystal display device according to claim2, wherein the plurality of pixel electrodes are disposed over thesecond insulating layer.
 7. A liquid crystal display device according toclaim 6, wherein a part of the second insulating layer is disposedbetween the part of each of the plurality of gate signal line disposedoutside of the plurality pixel regions and the second transparentconductive layer.